Exhibit 10.13

Loan Modification Agreement

This Loan
Modification Agreement (Agreement) is made this 26thday of June, 2006, by and between BANK OF
AMERICA, N.A. organized and existing under the laws of the United States of America with offices at 100 Federal Street, Boston, Massachusetts 02110 (the Bank) and OPNET TECHNOLOGIES, INC. a Delaware Corporation with an
address at 7255 Woodmont Avenue, Bethesda, Maryland 20814 (the Borrower).

RECITALS

WHEREAS, Reference is made to a certain loan arrangement (the Loan Arrangement) between the Bank and the Borrower evidenced by,
among any other documents, instruments, and agreements, (i) a certain Promissory Note, dated June 10, 2005 in favor of the Bank in the original principal amount of Two Million Six Hundred Thousand ($2,600,000.00) Dollars as amended from
time to time (the Note) and (ii) a Business Loan Agreement dated June 20, 2005, between the Borrower and the Bank and (iii) a Security Agreement dated June 10, 2002 as amended from time to time (the
Security Agreement) and (iv) UCC-1 Financing Statement (Financing Statement) bearing file number 2219573 and filed with the Delaware Secretary of State. The Note, the Loan Agreement, and the Security
Agreement and the Financing Statement together with any and all other instruments, documents, contracts or agreements which evidence, secure or otherwise relate to the Borrowers obligations with respect to the Loan Arrangement, all as modified
by any prior amendment agreements are herein collectively referred to as the Loan Documents.

WHEREAS, the
Borrower has requested that the Bank agree to the modification of the Loan Documents to, among other things, the maturity date of the Note as hereinafter described, and the Bank has so agreed, but only upon the terms and conditions set forth
hereinafter.

AGREEMENT

NOW THEREFORE, for good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, it is hereby agreed by the Bank and the Borrower that the Loan Documents are amended effective as of June 30th, 2006, as follows:

1.        The above referenced Recitals are true and correct and are
incorporated herein by reference and made a part hereof. Capitalized terms used herein and not otherwise defined shall have the same meaning herein as in the Loan Agreement.

2.        The Note is amended to delete the paragraph entitled PAYMENT and to substitute the following therefore:

PAYMENT. Borrower will pay this loan in one payment of all outstanding
principal plus all accrued unpaid interest on June 30, 2007 (the Maturity Date). In addition, Borrower will pay regular monthly payments of all accrued unpaid interest due as of each payment date, beginning July 31st, 2006, with all subsequent interest payments to be due on the same day of each month after that until the Maturity Date.
Unless otherwise agreed or required by applicable law, payments will be applied first to any accrued unpaid interest; then to any late charges, and then to any unpaid collection costs. The annual interest rate for this Note is computed on a 365/360
basis; that is, by applying the ratio of the annual interest rate over a year of 360 days multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding. Borrower will pay Lender at
Lenders address shown above or at such other place as the Lender may designate in writing.



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3.    In all other respects, the Loan Documents, including, but not limited to, the Note, the Loan
Agreement, and the Security Agreement are hereby confirmed, reaffirmed and ratified and all terms and provisions not amended hereby shall remain in full force and effect. To the extent that any term and condition of any Loan Document is inconsistent
with the terms and provisions hereof, such Loan Document is hereby amended to reflect the modifications and amendments set forth in this Agreement.

4.    To induce the Bank to enter into this Agreement, the Borrower represents and warrants that (a) all the representations and warranties contained in the Loan Documents, after giving effect to the amendments and
modifications contemplated hereby are true and correct on and as of the date hereof as though made on and as of the date hereof; (b) as of the date hereof, the Borrower has no defenses, counterclaims, offsets or other claims against the Bank or any
of its officers, employees, agents, attorneys, predecessors, affiliates, or other representatives of any nature, relating to the Loan Arrangement; (c) no default or breach under any of the Loan Documents after giving effect to the amendments
contemplated hereby, and no event which the passage of time or giving of notice or both would constitute such a default or breach, exists on the date hereof; and (d) the security interest granted to the Bank in the Loan Documents remains a first
perfected security interest in the Collateral and neither Borrower nor any guarantor has done anything to impair said security interest and Borrower will take whatever steps Bank deems reasonably necessary to protect and preserve the said security
interest.

5.    This Agreement does not constitute a discharge, release or waiver of any of the Borrowers or any
Guarantors obligations or liabilities under the Loan Documents, or any other agreements to which the Bank and the Borrower and any guarantor are parties, all of which remain in full force and effect.

MISCELLANEOUS

1.    This
Agreement and the rights and obligations of the parties hereunder shall be deemed to be a document executed under seal and shall be construed and interpreted in accordance with the laws of the State of Maryland (excluding the laws applicable to
conflicts or choice of law).

2.    This Agreement shall be binding upon and inure to the benefit of the parties hereto, their
respective administrators, successors and assigns. This Agreement may only be amended in writing. This Agreement may be signed in as many counterparts as necessary or convenient, and by the different parties on separate counterparts, each of which,
when so executed, shall be deemed an original but all such counterparts shall constitute but one and the same agreement. Article and paragraph headings are for reference only and shall not affect the interpretation or meaning of any provisions of
this Agreement. If any part of this Agreement is not enforceable, the rest of the Agreement may be enforced. The Bank retains all rights, even if it makes a loan after default. If the Bank waives a default, it shall not be construed as a waiver of
any future default.

3.    The Borrower shall reimburse the Bank for any reasonable costs and attorneys fees incurred by the Bank
in connection with the execution of this Agreement and in connection with the enforcement or preservation of any rights or remedies under the Loan Documents. Further the Borrower indemnifies and holds the Bank harmless from any loss, liability,
damages, judgments, and costs of any kind relating to or arising directly or indirectly out of (a) this Agreement or any document, instrument or agreement required hereunder, (b) any credit extended or committed by the Bank to the Borrower under the
Loan Documents, and (c) any litigation or proceeding related to or arising out of this Agreement, any Loan Document evidencing and/or securing any such credit. This indemnity includes but is not limited to, attorneys fees (including the
allocated cost of in-house counsel). This indemnity extends to the Bank, its parent, subsidiaries and all of their directors, officers, employees, agents, successors, attorneys and assigns. This indemnity shall survive



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repayment of the Borrowers obligations to the Bank. All sums due to the Bank under this paragraph shall be
obligations of the Borrower, due and payable immediately without demand.

IN WITNESS WHEREOF, the parties have caused this Agreement to be
duly executed as of the day and year first above written.





| |  |                                      |  |  |  |                                                                   |  |                    
| |  | ------------------------------------ |  |  |  | ----------------------------------------------------------------- |  | -------------------
| |  | WITNESSES:                           |  |  |  | BANK: BANK OF AMERICA, successor
by merger to Fleet National Bank
| |  |                                      |  | 
| |  | /s/ Michael Shuhy                    |  |  |  | By:                                                               |  | /s/ John B. Desmond
| |  | Print Name: Michael Shuhy, Associate |  |  |  |                                                                   |  | John B. Desmond    

Its:

Managing Director(Duly Authorized)






| |  |                             |  |  |  |                                    |  |                  
| |  | --------------------------- |  |  |  | ---------------------------------- |  | -----------------
| |  |                             |  |  |  | BORROWER: OPNET TECHNOLOGIES,
INC.
| |  |                             |  | 
| |  | /s/ Mel Wesley              |  |  |  | By:                                |  | /s/ Marc A. Cohen
| |  | Print Name: Mel Wesley, CFO |  |  |  |                                    |  | Marc A. Cohen    

Its:

CEO(Duly Authorized)




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