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                                 THIRD AMENDMENT
                                       TO
                    REVOLVING CREDIT AGREEMENT (UNGUARANTEED)
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         Third  Amendment  dated as of  October  25,  1999 to  Revolving  Credit
Agreement  (the  "Second  Amendment"),  by and among  APPNET  SYSTEMS,  INC.,  a
Delaware  corporation (the "Borrower"),  BANKBOSTON,  N.A. and the other lending
institutions  listed on  Schedule  1 to the  Credit  Agreement  (as  hereinafter
defined) (the  "Banks"),  amending  certain  provisions of the Revolving  Credit
Agreement  dated as of January 8, 1999 (as  amended  and in effect  from time to
time, the "Credit Agreement") by and among the Borrower, the Banks,  BankBoston,
N.A. as agent for the Banks (the  "Agent") and Antares  Capital  Corporation  as
co-agent for the Banks.  Terms not otherwise defined herein which are defined in
the Credit Agreement shall have the same respective meanings herein as therein.

         WHEREAS, the Borrower and the Banks have agreed to modify certain terms
and conditions of the Credit  Agreement as specifically  set forth in this Third
Amendment;

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

         ss.1. Amendment to Section 1.1 of the Credit Agreement.  Section 1.1 of
the Credit Agreement is hereby amended as follows:

         (a) The  definition  of  "EBITDA"  contained  in ss.1.1  of the  Credit
Agreement  is hereby  amended by deleting  such  definition  in its entirety and
restating it as follows:

                  EBITDA. With respect to the Borrower and its Subsidiaries
         for any fiscal period,  an amount equal to Consolidated Net Income
         for such period,  plus, to the extent  deducted in the calculation
         of Consolidated Net Income and without duplication, (a) income tax
         expense for such period;  (b) Consolidated  Total Interest Expense
         paid or accrued  (excluding  accrued interest the payment of which
         is  deferred  beyond  one year from the date such  amount is being
         determined)  during such period; (c) depreciation and amortization
         for such period;  (d) the one-time  expense incurred in the fiscal
         quarter  ended  September  30, 1999  pertaining  to the  severance
         arrangements  for  certain  employees;  and (e) the  amount of any
         earn-out or  noncompete  for such period to the extent such amount
         was capitalized and treated as debt (including  without limitation
         any earn-out such as that which was part of the  consideration  in
         the acquisition of New Media Publishing, Inc., which earn-out was

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         accounted for as compensation and noncompete and capitalized as an
         intangible asset and amortized), and minus, to the extent added in
         computing  Consolidated  Net Income and without  duplication,  all
         noncash gains (including income tax benefits) for such period, all
         as determined in accordance  with  generally  accepted  accounting
         principles.

         (b) Section 1.1 of the Credit Agreement is further amended by inserting
the following definition in the appropriate alphabetical order:

                  Earn-Out  Payments.  With respect to the Borrower and its
         Subsidiaries for any fiscal period, that amount which would appear
         on the  Borrower's  balance sheet as the line item for the accrued
         cash  amount  of the  present  value  of any  acquisition  related
         earn-outs and/or contingent compensation liabilities owed or to be
         owed by the Borrower or any  Subsidiary,  as  determined  for such
         period calculated in accordance with generally accepted accounting
         principles and in accordance  with the Borrower's  past accounting
         practices, consistently applied.

                  Total   Debt  to  EBITDA   Ratio.   As  at  any  date  of
         determination, the ratio of (a) Total Indebtedness of the Borrower
         and its Subsidiaries outstanding on such date to (b) EBITDA of the
         Borrower and its  Subsidiaries  for the Reference Period ending as
         of  the  most  recent  quarter  ended,  provided,   however,  when
         calculating the Total Debt to EBITDA Ratio for any period in which
         a Permitted Acquisition has occurred, the calculation of the Total
         Debt to EBITDA Ratio shall be made on a Pro Forma Basis.

                  Total Indebtedness.  All Indebtedness of the Borrower and
         its Subsidiaries for borrowed money (including without limitation,
         the  Earn-Out  Payments,  the  Seller  Subordinated  Debt  and all
         guarantees by such Person of  Indebtedness  of others for borrowed
         money),   purchase   money   Indebtedness   and  with  respect  to
         Capitalized  Leases and synthetic leases (as defined in clause (f)
         of the definition of "Indebtedness"), determined on a consolidated
         basis in accordance with generally accepted accounting principles.

         ss.2.  Amendment to Section 10 of the Credit  Agreement.  Section 10 of
the Credit  Agreement  is hereby  amended by deleting  ss.10 in its entirety and
restating ss.10 as follows:

                  10. FINANCIAL COVENANTS OF THE BORROWER.

                  The Borrower  covenants  and agrees that,  so long as any
         Revolving Credit Loan, Unpaid Reimbursement Obligation,  Letter of
         Credit or Revolving Credit Note is outstanding or any Bank has any
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                                    -3-


         obligation to make any Revolving Credit Loans or the Agent has any
         obligation to issue, extend or renew any Letters of Credit:

                  10.1  Leverage  Ratio.  The Borrower  will not permit the
         Leverage  Ratio at any time from (a) October 25, 1999 through June
         30,  2000 to exceed  2.25:1.00;  and (b) from July 1, 2000 and any
         time thereafter to exceed 2:00:1.00.

                  10.2 Minimum EBITDA. The Borrower will not, as of the end
         of any fiscal  quarter  ending during any period  described in the
         table set forth  below,  permit  EBITDA  of the  Borrower  and its
         Subsidiaries  for the fiscal  quarter  ending on such date,  to be
         less than the amount set forth opposite such period in such table:

         -----------------------------------------------------------------------
                      Fiscal Quarter
                         Ending                           Minimum EBITDA
         -----------------------------------------------------------------------
                    September 30, 1999                      $2,000,000
         -----------------------------------------------------------------------
                    December 31, 1999                       $1,500,000
         -----------------------------------------------------------------------
                    March 31, 2000 and                      $2,000,000
                    each fiscal quarter
                    ending thereafter
         -----------------------------------------------------------------------

                  10.3.  Consolidated  Operating  Cash  Flow to Total  Debt
         Service.  The Borrower  will not permit the ratio of  Consolidated
         Operating  Cash Flow to Total Debt Service for any fiscal  quarter
         ending on or after June 30,  1999  other  than the fiscal  quarter
         ending December 31, 1999 to be less than 1.50:1.00 for such fiscal
         quarter,  and will not permit the ratio of Consolidated  Operating
         Cash Flow to Total  Debt  Service  for the fiscal  quarter  ending
         December  31,  1999 to be less  than  0.60:1.00  for  such  fiscal
         quarter;  provided,  however, solely for the fiscal quarter ending
         December  31,  1999,  Total Debt  Service  shall not  include  any
         mandatory  payments of principal on the Seller  Subordinated  Debt
         consisting of the  convertible  promissory  note issued by Century
         Computing,  Incorporated  in  the  original  principal  amount  of
         $2,000,000.

                  10.4.  Consolidated  Operating  Cash Flow to Senior  Debt
         Service.  The Borrower  will not permit the ratio of  Consolidated
         Operating  Cash Flow to Senior Debt Service for any fiscal quarter
         ending on or after December 31, 1998 to be less than 2.00:1.00 for
         such fiscal quarter.

                  10.5. Quick Ratio. The Borrower will not permit the ratio
         of Consolidated Quick Assets to Consolidated  Current  Liabilities
         to be less than (a)  1.25:1.00  at any time from  August 16,  1999
         through and including  September 30, 1999 and (b) 0.90:1.00 at any
         time thereafter.
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                                    -4-


                  10.6. No Quarterly Net Loss. The Borrower will not permit
         Consolidated  Net Income  for any  fiscal  quarter to be less than
         $1.00.

                  10.7. Capital  Expenditures.  The Borrower will not make,
         or  permit  any  Subsidiary  of  the  Borrower  to  make,  Capital
         Expenditures,  other than Capital  Expenditures which the Majority
         Banks  reasonably  determine  are made for  nonrecurring  one-time
         infrastructure  purchases or leases by the Borrower, in any fiscal
         year that exceed, in the aggregate,  (a) $3,000,000 for the fiscal
         year ending  December 31, 1999;  and (b) $4,000,000 for the fiscal
         year ending thereafter.

                  10.8. Total Debt/EBITDA. The Borrower will not permit the
         Total Debt to EBITDA  Ratio (a) from October 25, 1999 through June
         29, 2000 to exceed  5.00:1.00 at any time;  (b) from June 30, 2000
         through December 30, 2000 to exceed 3.50:1.00 at any time; and (c)
         from December 31, 2000 and any time thereafter to exceed 3.00:1.00
         at any time.

         ss.3.  Conditions  to  Effectiveness.  This Third  Amendment  shall not
become effective until the Agent receives a counterpart of this Third Amendment,
executed by the Borrower, each Subsidiary and the Banks

         ss.4.  Representations  and Warranties.  The Borrower hereby represents
that, on and as of the date hereof,  each of the  representations and warranties
made by it in ss.7 of the Credit  Agreement  remain  true as of the date  hereof
(except to the extent of changes  resulting from  transactions  contemplated  or
permitted  by the Credit  Agreement  and the other Loan  Documents  and  changes
occurring in the ordinary course of business that singly or in the aggregate are
not  materially  adverse,  and to  the  extent  that  such  representations  and
warranties relate expressly to an earlier date),  provided,  that all references
therein to the Credit  Agreement shall refer to such Credit Agreement as amended
hereby.  In  addition,  the Borrower  hereby  represents  and warrants  that the
execution  and  delivery  by the  Borrower  and its  Subsidiaries  of this Third
Amendment and the performance by the Borrower and its Subsidiaries of all of its
agreements  and  obligations  under the  Credit  Agreement  and the  other  Loan
Documents as amended  hereby are within the  corporate  authority of each of the
Borrower and its  Subsidiaries  and has been duly  authorized  by all  necessary
corporate action on the part of the Borrower and its Subsidiaries.

         ss.5. Ratification, Etc. Except as expressly amended hereby, the Credit
Agreement  and  all  documents,  instruments  and  agreements  related  thereto,
including,  but not limited to the Security  Documents,  are hereby ratified and
confirmed  in all  respects  and shall  continue in full force and  effect.  The
Credit  Agreement  and this Third  Amendment  shall be read and  construed  as a
single  agreement.  All  references  in the  Credit  Agreement  or  any  related
agreement or instrument to the Credit  Agreement  shall  hereafter  refer to the
Credit Agreement as amended hereby.
<PAGE>
                                      -5-


         ss.6. No Waiver. Nothing contained herein shall constitute a waiver of,
impair or otherwise affect any Obligations, any other obligation of the Borrower
or any rights of the Agent or the Banks consequent thereon.

         ss.7. Counterparts. This Third Amendment may be executed in one or more
counterparts, each of which shall be deemed an original but which together shall
constitute one and the same instrument.

         ss.8.  Governing  Law. THIS THIRD  AMENDMENT  SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE  WITH,  THE LAWS OF THE  COMMONWEALTH  OF  MASSACHUSETTS
(WITHOUT REFERENCE TO CONFLICT OF LAWS).


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                                      -6-


         IN  WITNESS  WHEREOF,  the  parties  hereto  have  executed  this Third
Amendment as a document under seal as of the date first above written.

                                        APPNET SYSTEMS, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:

                                        BANKBOSTON, N.A.



                                        By: /s/
                                           ------------------------------------
                                           Jay L. Massimo, Director


                                        ANTARES CAPITAL CORPORATION



                                        By: /s/
                                           ------------------------------------
                                        Title:
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                                      -7-


                            RATIFICATION OF GUARANTY

         Each of the undersigned  guarantors hereby acknowledges and consents to
the foregoing Third Amendment as of October 25, 1999 and agrees that each of the
Guaranty dated as of January 8, 1999, March 4, 1999 and March 10, 1999 from each
of the undersigned  guarantors remains in full force and effect, and each of the
guarantors confirms and ratifies all of its obligations thereunder.

                                        APPNET OF MICHIGAN, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:

                                        APPNET OF MARYLAND, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SOFTWARE SERVICES CORPORATION



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        NEW MEDIA PUBLISHING, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        RESEARCH & PLANNING, INC.


                                        By: /s/
                                           ------------------------------------
                                        Title:
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                                      -8-


                                        CENTURY COMPUTING, INCORPORATED



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        THE KODIAK GROUP, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        I33 COMMUNICATION CORP.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SIGMA6, INC.



                                        By: /s/
                                           ------------------------------------
                                        Title:


                                        SALZINGER ACQUISITION CORP.



                                        By: /s/
                                           ------------------------------------
                                        Title: