<PAGE>

                                                                   Exhibit 10.17

                                                                  EXECUTION COPY

                        AMENDMENT NO. 1 dated as of January 13, 2000 (this
                  "Amendment"), to the CREDIT AGREEMENT dated as of June 23,
                  1999, (the "Credit Agreement"), among ANTEON CORPORATION, a
                  Virginia corporation (the "Borrower"), the Lenders (as defined
                  in Article 1 of the Credit Agreement), CREDIT SUISSE FIRST
                  BOSTON, a bank organized under the laws of Switzerland, acting
                  through its New York branch, as an Issuing Bank (as defined in
                  Article I of the Credit Agreement), and as administrative
                  agent (in such capacity, the "Administrative Agent") for the
                  Lenders, MELLON BANK, N.A., a national banking association, as
                  syndication agent (in such capacity, the "Syndication Agent"),
                  as swingline lender (in such capacity, the "Swingline
                  Lender"), and as collateral agent (in such capacity, the
                  "Collateral Agent") for the Lenders, and DEUTSCHE BANK AG, New
                  York Branch, as documentation agent (in such capacity, the
                  "Documentation Agent").

      A. Pursuant to the Credit Agreement, the Lenders and the Issuing Bank have
extended, and have agreed to extend, credit to the Borrower.

      B. The Borrower has requested that the Required Lenders agree to amend the
Credit Agreement as provided herein to allow the Borrower, among other things,
to sell and finance Third Party Government Receivables (as defined below).

      C. The Required Lenders are willing so to amend the Credit Agreement
pursuant to the terms and subject to the conditions set forth herein.

      D. Capitalized terms used but not defined herein shall have the meanings
assigned to them in the Credit Agreement.

      Accordingly, in consideration of the mutual agreements herein contained
and other good and valuable consideration, the sufficiency and receipt of which
are hereby acknowledged, the parties hereto agree as follows:

      SECTION 1. Amendments to Section 1.01. (a) The following definitions are
hereby inserted into Section 1.01 of the Credit Agreement in the appropriate
alphabetical order:

            ""Third Party Financing" shall mean the purchase on a nonrecourse
      basis from the Borrower or any Subsidiary of Third Party Government
      Receivables by a person that is not an Affiliate of the Borrower."

<PAGE>

            ""Third Party Government Receivables" shall mean all Accounts of the
      Borrower or any Subsidiary with respect to which the Account Debtor is the
      Government, which arise pursuant to a Third Party Sale and which are sold
      pursuant to a Third Party Financing."

            ""Third Party Sale" shall mean the sale to the Government by the
      Borrower or any Subsidiary of products and/or services acquired from or to
      be provided by, respectively, a person that is not the Borrower or an
      Affiliate of the Borrower, so long as the Account arising therefrom is
      promptly sold pursuant to a Third Party Financing."

      (b) The definition of "Asset Sale" in Section 1.01 of the Credit Agreement
is hereby amended and restated to read as follows:

            ""Asset Sale" shall mean the sale, transfer or other disposition (by
      way of merger, casualty, condemnation or otherwise) by the Borrower or any
      of the Subsidiaries to any person other than the Borrower or any
      Subsidiary Guarantor of (a) any Equity Interests of any of the
      Subsidiaries (other than directors' qualifying shares) or (b) any other
      assets of the Borrower or any of the Subsidiaries (other than (i)
      inventory, excess, damaged, obsolete or worn out assets, scrap and
      Permitted Investments, in each case disposed of in the ordinary course of
      business, (ii) dispositions between or among Foreign Subsidiaries, (iii)
      dispositions of Approved Margin Stock or (iv) dispositions of Third Party
      Government Receivables pursuant to any Third Party Financing), provided
      that any asset sale or series of related asset sales described in clause
      (b) above having a value not in excess of $250,000 shall be deemed not to
      be an "Asset Sale" for purposes of this Agreement."

      (c) The definition of "Ineligible Receivables" in Section 1.01 of the
Credit Agreement is hereby amended by (i) deleting the word "or" at the end of
clause (e) thereof and (ii) deleting the period at the end thereof and
substituting therefor the phrase ";or (g) Third Party Government Receivables."

      SECTION 2. Amendment to Section 6.02. Section 6.02 of the Credit Agreement
is hereby amended by (a) deleting the word "and" at the end of paragraph (k)
thereof, (b) deleting the period at the end of paragraph (1) thereof and
substituting "; and" therefor and (c) adding the following paragraph at the end
thereof:

      "(m) any Lien on Third Party Government Receivables purporting to be sold
      pursuant to a Third Party Financing in favor of the provider thereof."

      SECTION 3. Further Assurances. The Required Lenders hereby authorize the
Agents to execute any and all further documents, financing statements, releases,
agreements and instruments as the Borrower may reasonably request in order to
effectuate any Third Party Financing as contemplated by this Amendment.

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                                                                               3


      SECTION 4. Representations and Warranties. To induce the other parties
hereto to enter into this Amendment, the Borrower represents and warrants to
each of the Lenders, the Administrative Agent, the Issuing Banks, the Collateral
Agent and the Documentation Agents that, after giving effect to this Amendment,
(a) the representations and warranties set forth in Article III of the Credit
Agreement are true and correct in all material respects on and as of the date
hereof, except to the extent such representations and warranties expressly
relate to an earlier date, and (b) no Default or Event of Default has occurred
and is continuing.

      SECTION 5. Effectiveness. This Amendment shall become effective as of the
date first written above on the date on which the Administrative Agent shall
have received counterparts of this Amendment that, when taken together, bear the
signatures of the Borrower, the Guarantors and the Required Lenders.

      SECTION 6. Effect of Amendment. Except as expressly set forth herein, this
Amendment shall not by implication or otherwise limit, impair, constitute a
waiver of, or otherwise affect the rights and remedies of the Lenders, the
Issuing Banks, the Collateral Agent, the Administrative Agent or the
Documentation Agents under the Credit Agreement or any other Loan Document, and
shall not alter, modify, amend or in any way affect any of the terms,
conditions, obligations, covenants or agreements contained in the Credit
Agreement or any other Loan Document, all of which are ratified and affirmed in
all respects and shall continue in full force and effect. Nothing herein shall
be deemed to entitle any Loan Party to a consent to, or a waiver, amendment,
modification or other change of, any of the terms, conditions, obligations,
covenants or agreements contained in the Credit Agreement or any other Loan
Document in similar or different circumstances. This Amendment shall apply and
be effective only with respect to the provisions of the Credit Agreement
specifically referred to herein. After the date hereof, any reference to the
Credit Agreement shall mean the Credit Agreement, as modified hereby. This
Amendment shall constitute a "Loan Document" for all purposes of the Credit
Agreement and the other Loan Documents.

      SECTION 7. Counterparts. This Amendment may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed and delivered shall be deemed an original, but all such
counterparts together shall constitute but one and the same contract. Delivery
of an executed counterpart of a signature page of this Amendment by facsimile
transmission shall be as effective as delivery of a manually executed
counterpart hereof.

      SECTION 8. Applicable Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

      SECTION 9. Headings. The headings of this Amendment are for purposes of
reference only and shall not limit or otherwise affect the meaning hereof.

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                                                                               4


      SECTION 10. Expenses. The Borrower agrees to reimburse the Administrative
Agent for all out-of-pocket expenses in connection with this Amendment,
including the reasonable fees, charges and disbursements of Cravath, Swaine &
Moore, counsel for the Administrative Agent.

      SECTION 11. Acknowledgment of Guarantors. Each of the Guarantors hereto
hereby acknowledges receipt and notice of, and consents to the terms of, this
Amendment.

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                                                                               5


            IN W1TNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed by their duly authorized officers, all as of the date and year
first above written.

                                             ANTEON CORPORATION,

                                                by  /s/ Carlton B. Crenshaw
                                                   -----------------------------
                                                   Name:  Carlton B. Crenshaw
                                                   Title: Sr. V.P. Finance and
                                                          Admin.


                                             ANALYSIS & TECHNOLOGY, INC.,

                                                by  /s/ Carlton B. Crenshaw
                                                   -----------------------------
                                                   Name:  Carlton B. Crenshaw
                                                   Title: Vice President


                                             INTERACTIVE MEDIA CORP.,

                                                by  /s/ David M. Nolf
                                                   -----------------------------
                                                   Name:  David M. Nolf
                                                   Title: Secretary


                                             TECHMATICS, INC.,

                                                by  /s/ Carlton B. Crenshaw
                                                   -----------------------------
                                                   Name:  Carlton B. Crenshaw
                                                   Title: Vice President


                                             VECTOR DATA SYSTEMS, INC.

                                                by  /s/ Carlton B. Crenshaw
                                                   -----------------------------
                                                   Name:  Carlton B. Crenshaw
                                                   Title: Vice President

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION: __________________________

                     by _______________________
                        Name:
                        Title:

<PAGE>

            IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed by their duly authorized officers, all as of the date and year
first above written.

                                   ANTEON CORPORATION,

                                   by  /s/ Carlton B. Crenshaw
                                      ---------------------------------
                                      Name:  Carlton B. Crenshaw
                                      Title: Sr. V.P. Finance and Admin.

                                   CREDIT SUISSE FIRST BOSTON, individually
                                   and as Administrative Agent and Issuing Bank,

                                   by /s/ ROBERT HETU
                                      ---------------------------------
                                      Name: ROBERT HETU
                                      Title: VICE PRESIDENT

                                   by /s/ Joel Glodowski
                                      ---------------------------------
                                      Name: Joel Glodowski
                                      Title: Managing Director


                                   MELLON BANK, N.A., individually and as
                                   Collateral Agent, Swingline Lender and
                                   Syndication Agent,

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:

<PAGE>

                                   CREDIT SUISSE FIRST BOSTON, individually
                                   and as Administrative Agent and Issuing Bank,

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:


                                   MELLON BANK, N.A., individually and as
                                   Collateral Agent, Swingline Lender and
                                   Syndication Agent,

                                   by /s/ David Reed
                                      ---------------------------------
                                      Name: David Reed
                                      Title: 1st Vice President


                                   DEUTSCHE BANK AG, New York Branch, as
                                   Documentation Agent,

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:


                                   DEUTSCHE BANK AG, New York and/or
                                   Cayman Islands Branches, as Lender,

                                   by
                                      ---------------------------------
                                      Name:
                                      Title:

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION:
                     ------------------------------------
                     FLEETNATIONAL BANK
                     BOSTON, MASSACHUSETTS


                     by /s/ Roger C. Boucher
                        ---------------------------------
                        Name: Roger C. Boucher
                        Title: Senior Vice President

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION: IBM Credit Corporation
                     ------------------------------------


                     by /s/ Ronald J. Bachner
                        ---------------------------------
                        Name: Ronald J. Bachner,
                        Title: Manager, Commercial Financing
                               Solutions Americas

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION: PNC BANK, NATIONAL ASSOCIATION
                     ------------------------------------


                     by /s/ Daniel J. Paull
                        ---------------------------------
                        Name: Daniel J. Paull
                        Title: Vice President

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION: TRANSAMERICA BUSINESS CREDIT CORPORATION
                     ------------------------------------


                     by /s/ Perry Vavoules
                        ---------------------------------
                        Name: Perry Vavoules
                        Title: Senior Vice President

<PAGE>

                                                              SIGNATURE PAGE TO
                                                              AMENDMENT NO. 1
                                                              DATED AS OF
                                                              JANUARY 13, 2000
                                                              TO ANTEON
                                                              CORPORATION CREDIT
                                                              AGREEMENT

NAME OF INSTITUTION: BANK POLSKA KASA OPIEKI S.A., NEW YORK BRANCH
                     ------------------------------------


                     by /s/ HUSSEIN B. EL-TAWIL
                        ---------------------------------
                        Name: HUSSEIN B. EL-TAWIL
                        Title: VICE PRESIDENT