Document:

<PAGE>
                                                                    EXHIBIT 10.1

[BANK OF AMERICA LOGO APPEARS HERE]

                                 LOAN AGREEMENT

     This Loan Agreement (the "Agreement") dated as of June 10, 2002, by and
between Bank of America, N.A., a national banking association ("Bank") and the
Borrower described below.

     In consideration of the Loan or Loans described below and the mutual
covenants and agreements contained herein, and intending to be legally bound
hereby, Bank and Borrower agree as follows:

     1. DEFINITIONS AND REFERENCE TERMS. In addition to any other terms defined
herein, the following terms shall have the meaning set forth with respect
thereto:

          A.   Borrower: OPNET Technologies, Inc.
                        -------------------------------------------
               a(n)      Delaware corporation
                   ------------------------------------------------

          B.   Borrower's Address:

                              7255 Woodmont Avenue, Suite 250
               ----------------------------------------------------
                              Bethesda, Maryland 20814
               ----------------------------------------------------

          C. Hazardous Materials. Hazardous Materials include all materials
defined as hazardous materials or substances under any local, state or federal
environmental laws, rules or regulations, and petroleum, petroleum products, oil
and asbestos.

          D. Loan. Any loan described in Section 2 hereof and any subsequent
loan which states that it is subject to this Loan Agreement.

          E. Loan Documents. Loan Documents means this Loan Agreement and any
and all promissory notes executed by Borrower in favor of Bank and all other
documents, instruments, guarantees, certificates and agreements executed and/or
delivered by Borrower, any guarantor or third party in connection with any Loan.

          F. Accounting Terms. All accounting terms not specifically defined or
specified herein shall have the meanings generally attributed to such terms
under generally accepted accounting principles ("GAAP"), as in effect from time
to time, consistently applied, with respect to the financial statements
referenced in Section 3.H. hereof.

     2. LOANS.
        -----

          A. Loan. Bank hereby agrees to make (or has made) one or more loans to
Borrower in the aggregate principal face amount of $ 10,000,000.00. The
obligation to repay the loans is evidenced by a promissory note or notes dated
June 10, 2002 (the promissory note or notes together with any and all renewals,
extensions or rearrangements thereof being hereafter collectively referred to as
the "Note") having a maturity date, repayment terms and interest rate as set
forth in the Note.

               i.   Revolving Credit Feature. The Loan provides for a revolving
line of credit (the "Line") under which Borrower may from time to time, borrow,
repay and re-borrow funds.

               ii.  Borrowing Base. The Line is subject to the following advance
formula: 80% of outstanding accounts receivable aged less than 90 days from
invoice.

               iii. Usage Fee. Borrower will pay hereafter on September 30, 2002
and on the last day of each quarter for the period from and including the date
the Line was established to and including the maturity date of the Line, a usage
fee at a rate per annum of .25% of the average daily unused portion of the Line
during such period. The Borrower may at any time upon written notice to the Bank
permanently reduce the amount of the Line at which time the obligation of the
Borrower to pay a usage fee shall thereupon correspondingly be reduced.

                                       -1-

<PAGE>

               iv. Letter of Credit Subfeature. As a subfeature under the Line,
Bank may from time to time up to and including June 10, 2004, issue letters of
credit for the account of Borrower (each, a "Letter of Credit" and collectively,
"Letters of Credit"); provided, however, that the form and substance of each
Letter of Credit shall be subject to approval by Bank in its sole discretion;
and provided further that the aggregate undrawn amount of all outstanding
Letters of Credit shall not at any time exceed $10,000,000.00. Each Letter of
Credit shall be issued for a term not to exceed 365 days, as designated by
Borrower, provided, however, that no Letter of Credit shall have an expiration
date subsequent to June 10, 2004. The undrawn amount of all Letters of Credit
plus any and all amounts paid by Bank in connection with drawings under any
Letter of Credit for which the Bank has not been reimbursed shall be reserved
under the Line and shall not be available for advances thereunder. Each draft
paid by Bank under a Letter of Credit shall be deemed an advance under the Line
and shall be repaid in accordance with the terms of the Line; provided however,
that if the Line is not available for any reason whatsoever, at the time any
draft is paid by Bank, or if advances are not available under the Line in such
amount due to any limitation of borrowing set forth herein, then the full amount
of such drafts shall be immediately due and payable, together with interest
thereon, from the date such amount is paid by Bank to the date such amount is
fully repaid by Borrower, at that rate of interest applicable to advances under
the Line. In such event, Borrower agrees that Bank, at Bank's sole discretion
may debit Borrower's deposit account with Bank for the amount of such draft.

               v. Letter of Credit Fees. Letters of credit shall be assessed a
fee of 1.25% per annum, due upon issuance or a minimum fee of $500.00. All
amendment fees and transfer fees shall be due and payable by the Borrower.

     3. REPRESENTATIONS AND WARRANTIES. Borrower hereby represents and warrants
to Bank as follows:

          A. Good Standing. Borrower is a corporation, duly organized, validly
existing and in good standing under the laws of Delaware and has the power and
authority to own its property and to carry on its business in each jurisdiction
in which Borrower does business.

          B. Authority and Compliance. Borrower has full power and authority to
execute and deliver the Loan Documents and to incur and perform the obligations
provided for therein, all of which have been duly authorized by all proper and
necessary action of the appropriate governing body of Borrower. No consent or
approval of any public authority or other third party is required as a condition
to the validity of any Loan Document, and Borrower is in compliance with all
laws and regulatory requirements to which it is subject.

          C. Binding Agreement. This Agreement and the other Loan Documents
executed by Borrower constitute valid and legally binding obligations of
Borrower, enforceable in accordance with their terms.

          D. Litigation. There is no proceeding involving Borrower pending or,
to the knowledge of Borrower, threatened before any court or governmental
authority, agency or arbitration authority, except as disclosed to Bank in
writing and acknowledged by Bank prior to the date of this Agreement.

          E. No Conflicting Agreements. There is no charter, bylaw, stock
provision, partnership agreement or other document pertaining to the
organization, power or authority of Borrower and no provision of any existing
agreement, mortgage, indenture or contract binding on Borrower or affecting its
property, which would conflict with or in any way prevent the execution,
delivery or carrying out of the terms of this Agreement and the other Loan
Documents.

          F. Ownership of Assets. Borrower has good title to its assets, and its
assets are free and clear of liens, except those granted to Bank and as
disclosed to Bank in writing prior to the date of this Agreement.

          G. Taxes. All taxes and assessments due and payable by Borrower have
been paid or are being contested in good faith by appropriate proceedings and
the Borrower has filed all tax returns which it is required to file.

                                  -2-

<PAGE>

          H. Material Adverse Change. The financial statements of each Borrower
heretofore delivered to Bank have been prepared in accordance with GAAP applied
on a consistent basis throughout the period involved and fairly present each
Borrower's financial condition, including all material contingent liabilities as
of the date or dates thereof, and there has been no material adverse change in
the financial condition or operations of any Borrower since December 31, 2001.
All factual information furnished by each Borrower to Bank in connection with
this Agreement and any other loan documents executed in connection with this
Agreement is and will be accurate and complete on the date as of which such
information is delivered to Bank and is not and will not be incomplete by the
omission of any material fact necessary to make such information not misleading.

          I. Place of Business. Borrower's chief executive office is located at
7255 Woodmont Avenue, Suite 250 Bethesda, Maryland 20814

          J. Environmental. The conduct of Borrower's business operations and
the condition of Borrower's property does not and will not violate any federal
laws, rules or ordinances for environmental protection, regulations of the
Environmental Protection Agency, any applicable local or state law, rule,
regulation or rule of common law or any judicial interpretation thereof relating
primarily to the environment or Hazardous Materials.

          K. Continuation of Representations and Warranties. All representations
and warranties made under this Agreement shall be deemed to be made at and as of
the date hereof and at and as of the date of any advance under any Loan.

     4. AFFIRMATIVE COVENANTS. Until full payment and performance of all
obligations of Borrower under the Loan Documents, Borrower will, unless Bank
consents otherwise in writing (and without limiting any requirement of any other
Loan Document):

          A. Financial Condition. Maintain Borrower's financial condition as
follows, determined in accordance with GAAP applied on a consistent basis
throughout the period involved except to the extent modified by the following
definitions:

               i. Profitability. Maintain on a consolidated basis, a positive
net income before taxes and extraordinary items for each quarterly accounting
period.

               ii. Unencumbered Liquid Assets. Borrower shall hold Unencumbered
Liquid Assets having an aggregate market value of not less than Five Million and
00/100 Dollars ($5,000,000.00) at the Bank. For the purposes of this Agreement,
"Unencumbered Liquid Assets" shall mean the following assets owned by Borrower
(excluding assets of any retirement plan) which (i) are not the subject of any
lien, pledge, security interest or other arrangement with any creditor to have
his claim satisfied out of the asset (or proceeds thereof) prior to the general
creditors of Borrower, and (ii) may be converted to cash within five (5) days.

               iii. Funded Debt to EBITDA Ratio. Maintain on a consolidated
basis a ratio of Funded Debt to EBITDA not exceeding 2.5:1.0. "Funded Debt"
means all outstanding liabilities for borrowed money and other interest-bearing
liabilities, including current and long-term debt, capital leases, letters of
credit, Subordinated Liabilities, and any other contingent liabilities. "EBITDA"
means net income, less income or plus loss from discontinued operations and
extraordinary items, plus income taxes, plus interest expense, plus
depreciation, depletion, amortization and other non-cash charges. This ratio
will be calculated at the end of each reporting period for which Bank requires
financial statements from Borrower, using the results of the twelve-month period
ending with that reporting period. "Subordinated Liabilities" means liabilities
subordinated to Borrower's obligations to Bank in a manner acceptable to Bank in
its sole discretion.

          B. Financial Statements and Other Information. Maintain a system of
accounting satisfactory to Bank and in accordance with GAAP applied on a
consistent basis throughout the period involved, permit Bank's officers or
authorized representatives to visit and inspect Borrower's books of account and
other records at such reasonable times and as often as Bank may desire, and pay
the reasonable fees and disbursements of any accountants or other agents of Bank
selected by Bank for the foregoing purposes. Unless written notice of another
location is given to Bank, Borrower's books and records will be located at
Borrower's

                                  -3-

<PAGE>

chief executive office set forth above. All financial statements called for
below shall be prepared in accordance with GAAP and in form and content
acceptable to Bank.

In addition, Borrower will:

               i. Furnish to Bank audited financial statements, prepared in
accordance with GAAP and examined and certified by independent certified public
accountants reasonably satisfactory to the Bank, of Borrower for each fiscal
year of Borrower, within 120 days after the close of each such fiscal year, on a
consolidated basis.

               ii. Furnish to Bank internally prepared financial statements
(including a balance sheet and profit and loss statement) of Borrower for each
quarter of each fiscal year of Borrower, within 45 days after the close of each
such period, on a consolidated basis.

               iii. Furnish to Bank quarterly, a detailed accounts receivable
aging report, within 45 days after the close of each such period.

               iv. Furnish to Bank monthly, a borrowing base certificate, within
30 days after the close of each such period.

               v. Furnish to Bank a compliance certificate for (and executed by
an authorized representative of) Borrower concurrently with and dated as of the
date of delivery of each of the financial statements as required in paragraphs i
and ii above, containing (a) a certification that the financial statements of
even date are true and correct and that the Borrower is not in default under the
terms of this Agreement, and (b) computations and conclusions, in such detail as
Bank may request, with respect to compliance with this Agreement, and the other
Loan Documents, including computations of all quantitative covenants.

               vi. Furnish to Bank promptly upon transmission thereof, copies of
any filings, registrations, and reports to the SEC.

               vii. Furnish to Bank annually, a detailed two-year budget in form
reasonably satisfactory to Bank, including profit and loss statement and sources
and uses of cash.

               viii. Furnish to Bank promptly such additional information,
reports and statements respecting the business operations and financial
condition of Borrower respectively, from time to time, as Bank may reasonably
request.

          C. Insurance. Maintain insurance with responsible insurance companies
on such of its properties, in such amounts and against such risks as is
customarily maintained by similar businesses operating in the same vicinity,
specifically to include fire and extended coverage insurance covering all
assets, business interruption insurance, workers compensation insurance and
liability insurance, all to be with such companies and in such amounts as are
satisfactory to Bank and providing for at least 30 days prior notice to Bank of
any cancellation thereof. Satisfactory evidence of such insurance will be
supplied to Bank prior to funding under the Loan(s) and 30 days prior to each
policy renewal.

          D. Existence and Compliance. Maintain its existence, good standing and
qualification to do business, where required and comply with all laws,
regulations and governmental requirements including, without limitation,
environmental laws applicable to it or to any of its property, business
operations and transactions.

          E. Adverse Conditions or Events. Promptly advise Bank in writing of
(i) any condition, event or act which comes to its attention that would or might
materially adversely affect Borrower's financial condition or operations or
Bank's rights under the Loan Documents, (ii) any litigation filed by or against
Borrower, in excess of an aggregate amount of $250,000.00, (iii) any event that
has occurred that would constitute an event of default under any Loan Documents
and (iv) any uninsured or partially uninsured loss through fire, theft,
liability or property damage in excess of an aggregate of $250,000.00.

          F. Taxes and Other Obligations. Pay all of its taxes, assessments and
other obligations, including, but not limited to taxes, costs or other expenses
arising out of this transaction, as the same become due and payable, except to
the extent the same are being contested in good faith by appropriate proceedings
in

                                  -4-

<PAGE>

a diligent manner.

          G. Maintenance. Maintain all of its tangible property in good
condition and repair and make all necessary replacements thereof, and preserve
and maintain all licenses, trademarks, privileges, permits, franchises,
certificates and the like necessary for the operation of its business.

          H. Environmental. Immediately advise Bank in writing of (i) any and
all enforcement, cleanup, remedial, removal, or other governmental or regulatory
actions instituted, completed or threatened pursuant to any applicable federal,
state, or local laws, ordinances or regulations relating to any Hazardous
Materials affecting Borrower's business operations; and (ii) all claims made or
threatened by any third party against Borrower relating to damages,
contribution, cost recovery, compensation, loss or injury resulting from any
Hazardous Materials. Borrower shall immediately notify Bank of any remedial
action taken by Borrower with respect to Borrower's business operations.
Borrower will not use or permit any other party to use any Hazardous Materials
at any of Borrower's places of business or at any other property owned by
Borrower except such materials as are incidental to Borrower's normal course of
business, maintenance and repairs and which are handled in compliance with all
applicable environmental laws. Borrower agrees to permit Bank, its agents,
contractors and employees to enter and inspect any of Borrower's places of
business or any other property of Borrower at any reasonable times upon three
(3) days prior notice for the purposes of conducting an environmental
investigation and audit (including taking physical samples) to insure that
Borrower is complying with this covenant and Borrower shall reimburse Bank on
demand for the costs of any such environmental investigation and audit. Borrower
shall provide Bank, its agents, contractors, employees and representatives with
access to and copies of any and all data and documents relating to or dealing
with any Hazardous Materials used, generated, manufactured, stored or disposed
of by Borrower's business operations within five (5) days of the request
therefore.

          I. Maintain its primary depository relationship, including operating
accounts, with Bank of America.

     5. NEGATIVE COVENANTS. Until full payment and performance of all
obligations of Borrower under the Loan Documents, Borrower will not, without the
prior written consent of Bank (and without limiting any requirement of any other
Loan Documents):

          A. Disposal of Assets Outside Ordinary Course of Business. Sell,
assign, lease, transfer or otherwise dispose of any part of Borrower's business
or Borrower's assets, except in the ordinary course of Borrower's business.

          B. Change of Control. Cause, permit or suffer any change, direct or
indirect, in the Borrower's control. Control means at any time: (i) any "person"
or "group" (each as used in Sections 13(d)(3) and 14(d)(2) of the Exchange Act),
other than Persons owning 30% or more of the Voting Stock of the Borrower on the
Closing Date, either (A) becomes the "beneficial owner" (as defined in Rule
13d-3 of the Exchange Act), directly or indirectly, of Voting Stock of the
Borrower (or securities convertible into or exchangeable for such Voting Stock)
representing 30% or more of the combined voting power of all Voting Stock of the
Borrower (on a fully diluted basis) or (B) otherwise has the ability, directly
or indirectly, to elect a majority of the board of directors of the Borrower.

          C. Liens. Grant, suffer or permit any contractual or non-contractual
lien on or security interest in its assets, except in favor of Bank, and except
purchase money security interests not in excess of $500,000.00 in the aggregate,
or fail to promptly pay when due all lawful claims, whether for labor, materials
or otherwise.

          D. Extensions of Credit. Make or permit any subsidiary to make, any
loan or advance to any person or entity, or purchase or otherwise acquire, or
permit any subsidiary to purchase or other wise acquire, any capital stock,
assets, obligations, or other securities of, make any capital contribution, to
or otherwise invest in or acquire any interest in any entity, or participate as
a partner or joint venturer with any person or entity, in excess of $500,000.00
in the aggregate.

          E. Borrowings. Create, incur, assume or become liable in any manner
for any

                                  -5-

<PAGE>

indebtedness (for borrowed money, deferred payment for the purchase of assets,
lease payments, as surety or guarantor for the debt for another, or otherwise)
other than to Bank, except for normal trade debts incurred in the ordinary
course of Borrower's business, and except for existing indebtedness disclosed to
Bank in writing and acknowledged by Bank prior to the date of this Agreement,
with the exception of new purchase money indebtedness not in excess of
$500,000.00 in the aggregate.

          F. Dividends and Distributions. Make any distribution (other than
dividends payable in capital stock of Borrower) on any shares of any class of
its capital stock or, if Borrower is a partnership, make any distribution to any
partner, or apply any of its property or assets to the purchase, redemption or
other retirement of any shares of any class of capital stock of or any
partnership interest in Borrower.

          G. Permitted Investments. Have any existing, or make any new,
investments in any individual or entity, or make any capital contributions or
other transfers of assets to any individual or entity, except for investments in
any of the following: (i) certificates of deposit; (ii) U.S. treasury bills and
other obligations of the federal government; (iii) readily marketable securities
(including commercial paper, but excluding restricted stock and stock subject to
the provisions of Rule 144 of the Securities and Exchange Commission) rated at
least in the three highest categories by Standard & Poor's or at least in the
three highest categories by Moody's Investors Service, Inc.; (iv) repurchase
agreements covering U.S. government securities; (v) stocks or assets of
companies in complementary lines of business as long as the cash investment does
not exceed $10,000,000.00, in the aggregate, in any fiscal year and the proforma
financial statement demonstrates that the company will remain in compliance with
all covenants.

          H. Character of Business. Change the general character of business as
conducted at the date hereof, or engage in any type of business not reasonably
related to its business as presently conducted.

          I. Change of Management. Make any substantial change in its present
executive or management personnel.

          J. Suspend Business. Voluntarily liquidate, dissolve or suspend its
business.

     6. DEFAULT. Borrower shall be in default under this Agreement and under
each of the other Loan Documents if it shall default in the payment of any
amounts due and owing under the Loan and such default is not cured within five
(5) business days or should or should it fail to timely and properly observe,
keep or perform any term, covenant, agreement or condition in any Loan Document
if failure is not cured within 30 days or in any other loan agreement,
promissory note, security agreement, deed of trust, deed to secure debt,
mortgage, assignment or other contract securing or evidencing payment of any
indebtedness of Borrower to Bank or any affiliate or subsidiary of Bank of
America Corporation.

     7. REMEDIES UPON DEFAULT. If an event of default shall occur, Bank shall
have all rights, powers and remedies available under each of the Loan Documents
as well as all rights and remedies available at law or in equity.

     8. NOTICES. All notices, requests or demands which any party is required or
may desire to give to any other party under any provision of this Agreement must
be in writing delivered to the other party at the following address:

     Borrower:

          OPNET Technologies, Inc.
     ------------------------------------------
          7255 Woodmont Avenue, Suite 250
     ------------------------------------------
          Bethesda, Maryland 20814
     ------------------------------------------
     Fax. No.____________________________

     Bank: Bank of America, N.A.
           6610 Rockledge Drive
     ------------------------------------------
           Bethesda, Maryland 20817-1811
     ------------------------------------------

     Fax No. 301-517-3120
            ---------------

or to such other address as any party may designate by written notice to
the other party. Each such notice, request and demand shall be deemed given or
made as follows:

                                  -6-

<PAGE>

          A. If sent by mail, upon the earlier of the date of receipt or five
(5) days after deposit in the U.S. Mail, first class postage prepaid;

          B. If sent by any other means , upon delivery.

     9. COSTS, EXPENSES AND ATTORNEYS' FEES. Borrower shall pay to Bank
immediately upon demand the full amount of all reasonable and necessary costs
and expenses, including reasonable attorneys' fees (to include outside counsel
fees and all allocated costs of Bank's in-house counsel if permitted by
applicable law), incurred by Bank in connection with (a) negotiation and
preparation of this Agreement and each of the Loan Documents, and (b) all other
costs and attorneys' fees incurred by Bank for which Borrower is obligated to
reimburse Bank in accordance with the terms of the Loan Documents.

     10. MISCELLANEOUS. Borrower and Bank further covenant and agree as follows,
without limiting any requirement of any other Loan Document:

          A. Cumulative Rights and No Waiver. Each and every right granted to
Bank under any Loan Document, or allowed it by law or equity shall be cumulative
of each other and may be exercised in addition to any and all other rights of
Bank, and no delay in exercising any right shall operate as a waiver thereof,
nor shall any single or partial exercise by Bank of any right preclude any other
or future exercise thereof or the exercise of any other right. Borrower
expressly waives any presentment, demand, protest or other notice of any kind,
including but not limited to notice of intent to accelerate and notice of
acceleration. No notice to or demand on Borrower in any case shall, of itself,
entitle Borrower to any other or future notice or demand in similar or other
circumstances.

          B. Applicable Law. This Loan Agreement and the rights and obligations
of the parties hereunder shall be governed by and interpreted in accordance with
the laws of Maryland and applicable United States federal law.

          C. Amendment. No modification, consent, amendment or waiver of any
provision of this Loan Agreement, nor consent to any departure by Borrower
therefrom, shall be effective unless the same shall be in writing and signed by
an officer of Bank, and then shall be effective only in the specified instance
and for the purpose for which given. This Loan Agreement is binding upon
Borrower, its successors and assigns, and inures to the benefit of Bank, its
successors and assigns; however, no assignment or other transfer of Borrower's
rights or obligations hereunder shall be made or be effective without Bank's
prior written consent, nor shall it relieve Borrower of any obligations
hereunder. There is no third party beneficiary of this Loan Agreement.

          D. Documents. All documents, certificates and other items required
under this Loan Agreement to be executed and/or delivered to Bank shall be in
form and content satisfactory to Bank and its counsel.

          E. Partial Invalidity. The unenforceability or invalidity of any
provision of this Loan Agreement shall not affect the enforceability or validity
of any other provision herein and the invalidity or unenforceability of any
provision of any Loan Document to any person or circumstance shall not affect
the enforceability or validity of such provision as it may apply to other
persons or circumstances.

          F. Indemnification. Notwithstanding anything to the contrary contained
in Section 10(G), Borrower shall indemnify, defend and hold Bank and its
successors and assigns harmless from and against any and all claims, demands,
suits, losses, damages, assessments, fines, penalties, costs or other expenses
(including reasonable attorneys' fees and court costs) arising from or in any
way related to any of the transactions contemplated hereby, including but not
limited to actual or threatened damage to the environment, agency costs of
investigation, personal injury or death, or property damage, due to a release or
alleged release of Hazardous Materials, arising from Borrower's business
operations, any other property owned by Borrower or in the surface or ground
water arising from Borrower's business operations, or gaseous emissions arising
from Borrower's business operations or any other condition existing or arising
from Borrower's business operations resulting from the use or existence of
Hazardous Materials, whether such claim proves to be true or false. Borrower
further agrees that its indemnity obligations shall include, but are not limited
to, liability for damages resulting from the personal injury or death of an
employee of the Borrower, regardless of whether the Borrower has paid the
employee under the workmen's compensation laws of any state or other similar
federal or state

                                  -7-

<PAGE>

legislation for the protection of employees. The term "property damage" as used
in this paragraph includes, but is not limited to, damage to any real or
personal property of the Borrower, the Bank, and of any third parties. The
Borrower's obligations under this paragraph shall survive the repayment of the
Loan and any deed in lieu of foreclosure or foreclosure of any Deed to Secure
Debt, Deed of Trust, Security Agreement or Mortgage securing the Loan.

          G. Survivability. All covenants, agreements, representations and
warranties made herein or in the other Loan Documents shall survive the making
of the Loan and shall continue in full force and effect so long as the Loan is
outstanding or the obligation of the Bank to make any advances under the Line
shall not have expired.

     11. NO ORAL AGREEMENT. THIS WRITTEN LOAN AGREEMENT AND THE OTHER LOAN
DOCUMENTS REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS
OF THE PARTIES.

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed under seal by their duly authorized representatives as of the date
first above written.

BORROWER:  OPNET Technologies, Inc.         BANK:  Bank of America, N.A.
          --------------------------

By:____________________________ (SEAL)      By: _________________________(SEAL)
Name:__________________________             Name:  Robin D. Hartley
Title:_________________________             Title: Credit Officer

[Corporate Seal]

If the Borrower is a corporation, the signature should be attested by the
Secretary or Assistant Secretary of the corporation and the corporate seal
affixed.

Attest:_______________________(SEAL)
Name:
Title:

                                  -8-<PAGE>
                                                                    EXHIBIT 10.2

[BANK OF AMERICA LOGO APPEARS HERE]

                                 Promissory Note
                                                             Customer# 41-567249

<TABLE>
<S>                          <C>            <C>                      <C>
Date June 10, 2002 []New     [X]Renewal     Amount $10,000,000.00    Maturity Date June 10, 2004
     -------------                                 --------------                  -------------

================================================================================================
Bank:                                            Borrower:

Bank of America, N.A.
Banking Center:                                       OPNET Technologies, Inc.
                                                      7255 Woodmont Avenue, Suite 250
     Commercial Banking                               Bethesda, Maryland 20814
     6610 Rockledge Drive
     Bethesda, Maryland 20817-1811

     County:  Montgomery                              County: Montgomery

================================================================================================
</TABLE>

FOR VALUE RECEIVED, the undersigned Borrower unconditionally (and jointly and
severally, if more than one) promises to pay to the order of Bank, its
successors and assigns, without setoff, at its offices indicated at the
beginning of this Note, or at such other place as may be designated by Bank, the
principal amount of Ten Million and 00/100 Dollars ($10,000,000.00), or so much
thereof as may be advanced from time to time in immediately available funds,
together with interest computed daily on the outstanding principal balance
hereunder, at an annual interest rate, and in accordance with the payment
schedule, indicated below.

[This Note contains some provisions preceded by boxes. If a box is marked, the
provision applies to this transaction; if it is not marked, the provision does
not apply to this transaction.]

1. Rate.

See Attached Exhibit "A"

Notwithstanding any provision of this Note, Bank does not intend to charge and
Borrower shall not be required to pay any amount of interest or other charges in
excess of the maximum permitted by the applicable law of the State of Maryland;
if any higher rate ceiling is lawful, then that higher rate ceiling shall apply.
Any payment in excess of such maximum shall be refunded to Borrower or credited
against principal, at the option of Bank.

2. Accrual Method. Unless otherwise indicated, interest at the Rate set forth
above will be calculated by the 365/360 day method (a daily amount of interest
is computed for a hypothetical year of 360 days; that amount is multiplied by
the actual number of days for which any principal is outstanding hereunder). If
interest is not to be computed using this method, the method shall be: N/A.
                                                                       ---

3. Rate Change Date. Any Rate based on a fluctuating index or base rate will
change, unless otherwise provided, each time and as of the date that the index
or base rate changes. If the Rate is to change on any other date or at any other
interval, the change shall be: N/A. In the event any index is discontinued, Bank
                               ---
shall substitute an index determined by Bank to be comparable, in its sole
discretion.

4. Payment Schedule. All payments received hereunder shall be applied first to
the payment of any expense or charges payable hereunder or under any other loan
documents executed in connection with this Note, then to interest due and
payable, with the balance applied to principal, or in such other order as Bank
shall determine at its option.

Single Principal Payment. Principal shall be paid in full in a single payment on
June 10, 2004. Interest thereon shall be paid monthly, commencing on July 10,
2002, and continuing on the same day of each successive month, quarter or other
period (as applicable) thereafter, with a final payment of all unpaid interest
at the stated maturity of this Note.

5. Revolving Feature.

[X] Borrower may borrow, repay and reborrow hereunder at any time, up to a
maximum aggregate amount outstanding at any one time equal to the principal
amount of this Note, provided, that Borrower is not in default under any
provision of this Note, any other documents executed in connection with this
Note, or any other note or other loan documents now or hereafter executed in
connection with any other obligation of Borrower to Bank, and provided that the
borrowings hereunder do not exceed any borrowing base or other limitation on
borrowings by Borrower. Bank shall incur no liability for its refusal to advance
funds based upon its determination that any conditions of such further advances
have not been met. Bank records of the amounts borrowed from time to time shall
be conclusive proof thereof.

     [] Uncommitted Facility. Borrower acknowledges and agrees that,
     notwithstanding any provisions of this Note or any other documents executed
     in connection with this Note, Bank has no obligation to make any advance,
     and that all advances are at the sole discretion of Bank.

     [] Out-Of-Debt Period. For a period of at least __ consecutive days during
     [] each fiscal year, [] any consecutive 12-month period, Borrower shall
     fully pay down the balance of this Note, so that no amount of principal or
     interest and no other obligation under this Note remains outstanding.

6.   Automatic Payment.

[ ] Borrower has elected to authorize Bank to effect payment of sums due under
this Note by means of debiting Borrower's account number ______________________.
This authorization shall not affect the obligation of Borrower to pay such sums
when due, without notice, if there are insufficient funds in such account to
make such payment in full on the due date thereof, or if Bank fails to debit the
account.

                                       1

                                                              Approved: 09-21-95
                                                               Revised: 08-30-99

<PAGE>

7. Waivers, Consents and Covenants. Borrower, any endorser, or guarantor hereof
or any other party hereto (individually an "Obligor" and collectively
"Obligors") and each of them jointly and severally: (a) waive presentment,
demand, protest, notice of demand, notice of intent to accelerate, notice of
acceleration of maturity, notice of protest, notice of nonpayment, notice of
dishonor, and any other notice required to be given under the law to any Obligor
in connection with the delivery, acceptance, performance, default or enforcement
of this Note, any endorsement or guaranty of this Note, or any other documents
executed in connection with this Note or any other note or other loan documents
now or hereafter executed in connection with any obligation of Borrower to Bank
(the "Loan Documents"); (b) consent to all delays, extensions, renewals or other
modifications of this Note or the Loan Documents, or waivers of any term hereof
or of the Loan Documents, or release or discharge by Bank of any of Obligors, or
release, substitution or exchange of any security for the payment hereof, or the
failure to act on the part of Bank, or any indulgence shown by Bank (without
notice to or further assent from any of Obligors), and agree that no such
action, failure to act or failure to exercise any right or remedy by Bank shall
in any way affect or impair the obligations of any Obligors or be construed as a
waiver by Bank of, or otherwise affect, any of Bank's rights under this Note,
under any endorsement or guaranty of this Note or under any of the Loan
Documents; and (c) agree to pay, on demand, all costs and expenses of collection
or defense of this Note or of any endorsement or guaranty hereof and/or the
enforcement or defense of Bank's rights with respect to, or the administration,
supervision, preservation, protection of, or realization upon, any property
securing payment hereof, including, without limitation, reasonable attorney's
fees, including fees related to any suit, mediation or arbitration proceeding,
out of court payment agreement, trial, appeal, bankruptcy proceedings or other
proceeding, in the amount of 10% of the principal amount of this Note, or such
greater amount as may be determined reasonable by any arbitrator or court,
whichever is applicable.

8. Prepayments. Prepayments may be made in whole or in part at any time on any
loan for which the Rate is based on the Prime Rate or on any other fluctuating
Rate or index which may change daily. All prepayments of principal shall be
applied in the inverse order of maturity, or in such other order as Bank shall
determine in its sole discretion.

9. Delinquency Charge. To the extent permitted by law, a delinquency charge may
be imposed in an amount not to exceed four percent (4%) of any payment that is
more than fifteen days late.

10. Events of Default. The following are events of default hereunder: (a) the
failure to pay or perform any obligation, liability or indebtedness of any
Obligor to Bank, or to any affiliate or subsidiary of Bank of America
Corporation, whether under this Note or any Loan Documents, as and when due
(whether upon demand, at maturity or by acceleration) and not remedied or cured
as permitted in Section 6 under the Loan Agreement dated June 10, 2002; (b) the
failure to pay or perform any other obligation, liability or indebtedness of any
Obligor in excess of $1,000,000.00 to any other party; (c) the death of any
Obligor (if an individual); (d) the resignation or withdrawal of any material
owner/Guarantor of Borrower, as determined by Bank in its sole discretion; (e)
the commencement of a proceeding against any Obligor for dissolution or
liquidation, the voluntary or involuntary termination or dissolution of any
Obligor or the merger or consolidation of any Obligor with or into another
entity; (f) the insolvency of, the business failure of, the appointment of a
custodian, trustee, liquidator or receiver for or for any of the property of,
the assignment for the benefit of creditors by, or the filing of a petition
under bankruptcy, insolvency or debtor's relief law or the filing of a petition
for any adjustment of indebtedness, composition or extension by or against any
Obligor; (g) that any representation or warranty made to Bank by any Obligor in
any Loan Documents or otherwise was, when it was made, untrue or materially
misleading; (h) the failure of any Obligor to timely deliver such financial
statements, including tax returns, other statements of condition or other
information, as Bank shall request from time to time not remedied within five
(5) business days; (i) the entry of a judgment against any Obligor which Bank
deems to be of a material nature, in Bank's sole discretion not paid or
dismissed within thirty (30) days; (j) the seizure or forfeiture of, or the
issuance of any writ of possession, garnishment or attachment, or any turnover
order for any property of any Obligor; (k) the determination by Bank that it is
insecure for any reason; (l) the determination by Bank that a material adverse
change has occurred in the financial condition of any Obligor; or (m) the
failure of Borrower's business to comply with any material law or regulation
controlling its operation.

11. Remedies upon Default. Whenever there is a default under this Note (a) the
entire balance outstanding hereunder and all other obligations of any Obligor to
Bank (however acquired or evidenced) shall, at the option of Bank, become
immediately due and payable and any obligation of Bank to permit further
borrowing under this Note shall immediately cease and terminate, and/or (b) to
the extent permitted by law, the Rate of interest on the unpaid principal shall
be increased at Bank's discretion up to the Prime Rate plus 5% per annum (the
"Default Rate"). The provisions herein for a Default Rate shall not be deemed to
extend the time for any payment hereunder or to constitute a "grace period"
giving Obligors a right to cure any default. At Bank's option, any accrued and
unpaid interest, fees or charges may, for purposes of computing and accruing
interest on a daily basis after the due date of the Note or any installment
thereof, be deemed to be a part of the principal balance, and interest shall
accrue on a daily compounded basis after such date at the Default Rate provided
in this Note until the entire outstanding balance of principal and interest is
paid in full. Bank is hereby authorized at any time to set off and charge
against any deposit accounts of any Obligor, as well as any money, instruments,
securities, documents, chattel paper, credits, claims, demands, income and any
other property, rights and interests of any Obligor which at any time shall come
into the possession or custody or under the control of Bank or any of its
agents, affiliates or correspondents, without notice or demand, any and all
obligations due hereunder. Additionally, Bank shall have all rights and remedies
available under each of the Loan Documents, as well as all rights and remedies
available at law or in equity.

12. Non-waiver. The failure at any time of Bank to exercise any of its options
or any other rights hereunder shall not constitute a waiver thereof, nor shall
it be a bar to the exercise of any of its options or rights at a later date. All
rights and remedies of Bank shall be cumulative and may be pursued singly,
successively or together, at the option of Bank. The acceptance by Bank of any
partial payment shall not constitute a waiver of any default or of any of Bank's
rights under this Note. No waiver of any of its rights hereunder, and no
modification or amendment of this Note, shall be deemed to be made by Bank
unless the same shall be in writing, duly signed on behalf of Bank; each such
waiver shall apply only with respect to the specific instance involved, and
shall in no way impair the rights of Bank or the obligations of Obligor to Bank
in any other respect at any other time.

13. Applicable Law, Venue and Jurisdiction. This Note and the rights and
obligations of Borrower and Bank shall be governed by and interpreted in
accordance with the law of the State of Maryland. In any litigation in
connection with or to enforce this Note or any endorsement or guaranty of this
Note or any Loan Documents, Obligors, and each of them, irrevocably consent to
and confer personal jurisdiction on the courts of the State of Maryland or the
United States located within the State of Maryland and expressly waive any
objections as to venue in any such courts. Nothing contained herein shall,
however, prevent Bank from bringing any action or exercising any rights within
any other state or jurisdiction or from obtaining personal jurisdiction by any
other means available under applicable law.

14. Partial Invalidity. The unenforceability or invalidity of any provision of
this Note shall not affect the enforceability or validity of any other provision
herein and the invalidity or unenforceability of any provision of this Note or
of the Loan Documents to any person or circumstance shall not affect the
enforceability or validity of such provision as it may apply to other persons or
circumstances.

15. Waiver of Jury Trial. Obligors waive trial by jury in any action or
proceeding to which Obligors and Bank may be parties, arising out of, in
connection with or in any way pertaining to, this Note or the Loan Documents. It
is agreed and understood that this waiver constitutes a waiver of trial by jury
of all claims against all parties to such action or proceedings, including
claims against parties who are not parties to this Note. This waiver is
knowingly, willingly and voluntarily made by Obligors.

                                        2
                                                              Approved: 09-21-95
                                                               Revised: 08-30-99

<PAGE>

16. Binding Effect. This Note shall be binding upon and inure to the benefit of
Borrower, Obligors and Bank and their respective successors, assigns, heirs and
personal representatives, provided, however, that no obligations of Borrower or
Obligors hereunder can be assigned without prior written consent of Bank.

17. Controlling Document. To the extent that this Note conflicts with or is in
any way incompatible with any other Loan Document concerning this obligation,
the Note shall control over any other document, and if the Note does not address
an issue, then each other document shall control to the extent that it deals
most specifically with an issue.

18. ARBITRATION. ANY CONTROVERSY OR CLAIM BETWEEN OR AMONG THE PARTIES HERETO
INCLUDING BUT NOT LIMITED TO THOSE ARISING OUT OF OR RELATING TO THIS
INSTRUMENT, AGREEMENT OR DOCUMENT OR ANY RELATED INSTRUMENTS, AGREEMENTS OR
DOCUMENTS, INCLUDING ANY CLAIM BASED ON OR ARISING FROM AN ALLEGED TORT, SHALL
BE DETERMINED BY BINDING ARBITRATION IN ACCORDANCE WITH THE FEDERAL ARBITRATION
ACT (OR IF NOT APPLICABLE, THE APPLICABLE STATE LAW,) THE RULES OF PRACTICE AND
PROCEDURE FOR THE ARBITRATION OF COMMERCIAL DISPUTES OF J.A.M.S./ENDISPUTE OR
ANY SUCCESOR THEREOF (J.A.M.S.), AND THE "SPECIAL RULES" SET FORTH BELOW. IN THE
EVENT OF ANY INCONSISTENCY, THE SPECIAL RULES SHALL CONTROL. JUDGMENT UPON ANY
ARBITRATION AWARD MAY BE ENTERED IN ANY COURT HAVING JURISDICTION. ANY PARTY TO
THIS INSTRUMENT, AGREEMENT OR DOCUMENT MAY BRING AN ACTION, INCLUDING A SUMMARY
OR EXPEDITED PROCEEDING, TO COMPEL ARBITRATION OF ANY CONTROVERSY OR CLAIM TO
WHICH THIS AGREEMENT APPLIES IN ANY COURT HAVING JURISDICTION OVER SUCH ACTION.

A. SPECIAL RULES. THE ARBITRATION SHALL BE CONDUCTED IN THE COUNTY OF ANY
BORROWER'S DOMICILE AT THE TIME OF THE EXECUTION OF THIS INSTRUMENT, AGREEMENT
OR DOCUMENT AND ADMINISTERED BY J.A.M.S. WHO WILL APPOINT AN ARBITRATIOR; IF
J.A.M.S. IS UNABLE OR LEGALLY PRECLUDED FROM ADMINISTERING THE ARBITRATION, THEN
THE AMERICAN ARBITRATION ASSOCIATION WILL SERVE. ALL ARBITRATION HEARINGS WILL
BE COMMENCED WITHIN 90 DAYS OF THE DEMAND FOR ARBITRATION; FURTHER, THE
ARBITRATOR SHALL ONLY, UPON A SHOWING OF CAUSE, BE PERMITTED TO EXTEND THE
COMMENCEMENT OF SUCH HEARING FOR UP TO AN ADDITIONAL 60 DAYS.

B. RESERVATION OF RIGHTS. NOTHING IN THIS ARBITRATION PROVISION SHALL BE DEEMED
TO (I) LIMIT THE APPLICABILITY OF ANY OTHERWISE APPLICABLE STATUTES OF
LIMITATION OR REPOSE AND ANY WAIVERS CONTAINED IN THIS INSTRUMENT, AGREEMENT OR
DOCUMENT; OR (II) BE A WAIVER BY BANK OF THE PROTECTION AFFORDED TO IT BY 12
U.S.C. SEC. 91 OR ANY SUBSTANTIALLY EQUIVALENT STATE LAW; OR (III) LIMIT THE
RIGHT OF BANK HERETO (A) TO EXERCISE SELF HELP REMEDIES SUCH AS (BUT NOT LIMITED
TO) SETOFF, OR (B) TO FORECLOSE AGAINST ANY REAL OR PERSONAL PROPERTY
COLLATERAL, OR (C) TO OBTAIN FROM A COURT PROVISIONAL OR ANCILLARY REMEDIES SUCH
AS ( BUT NOT LIMITED TO) INJUNCTIVE RELIEF, WRIT OF POSSESSION OR THE
APPOINTMENT OF A RECEIVER. BANK MAY EXERCISE SUCH SELF HELP RIGHTS, FORECLOSE
UPON SUCH PROPERTY, OR OBTAIN SUCH PROVISIONAL OR ANCILLARY REMEDIES BEFORE,
DURING OR AFTER THE PENDENCY OF ANY ARBITRATION PROCEEDING BROUGHT PURSUANT TO
THIS INSTRUMENT, AGREEMENT OR DOCUMENT. NEITHER THIS EXERCISE OF SELF HELP
REMEDIES NOR THE INSTITUTION OR MAINTENANCE OF AN ACTION FOR FORECLOSURE OR
PROVISIONAL OR ANCILLARY REMEDIES SHALL CONSTITUTE A WAIVER OF THE RIGHT OF ANY
PARTY, INCLUDING THE CLAIMANT IN ANY SUCH ACTION, TO ARBITRATE THE MERITS OF THE
CONTROVERSY OR CLAIM OCCASIONING RESORT TO SUCH REMEDIES.

Borrower represents to Bank that the proceeds of this loan are to be used
primarily for business, commercial or agricultural purposes. Borrower
acknowledges having read and understood, and agrees to be bound by, all terms
and conditions of this Note, and hereby executes this Note intending to create
an instrument executed under seal.

NOTICE OF FINAL AGREEMENT. THIS WRITTEN PROMISSORY NOTE REPRESENTS THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS.

Corporate or Partnership Borrower

OPNET Technologies, Inc.
------------------------

By:___________________________  (Seal)

Name:_________________________

Title:________________________

______________________________
Attest (If Applicable)

[Corporate Seal]

                                        3
                                                              Approved: 09-21-95
                                                               Revised: 08-30-99

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