<PAGE>

                               SECOND AMENDMENT TO
                      AMENDED AND RESTATED CREDIT AGREEMENT

         This Second Amendment to Amended and Restated Credit Agreement
("Agreement") is made as of this 7th day of February, 1997 by and between PSINet
Inc. (f/k/a Performance Systems International, Inc.), a New York corporation
("PSI"), (PSI hereinafter sometimes referred to as "Borrower" or "Borrowers")
PSINet Pipeline New York, Inc., a New York corporation ("Pipeline"), as a
guarantor, and Fleet National Bank, formerly known as Fleet National Bank of
Connecticut, successor by merger to Fleet Bank of Massachusetts, N.A.
(hereinafter referred to as the "Bank"), as lender.

         WHEREAS, as of November 30, 1994, PSI and the Bank entered into a
Credit Agreement (the "Original Credit Agreement");

         WHEREAS, as of March 24, 1995, PSI and the Bank entered into an
amendment to the Original Credit Agreement (the "First Amendment to Credit
Agreement") to (i) increase the term credit from $2,000,000 to $8,500,000, (ii)
add the then newly-acquired Pipeline as a guarantor and (iii) otherwise amend
the Original Credit Agreement, all as set forth in the First Amendment to Credit
Agreement;

         WHEREAS, as of November 10, 1995, PSI, InterCon Systems Corporation
("InterCon"), Software Ventures Corporation ("Software") and the Bank entered
into an Amended and Restated Credit Agreement (the "Amended and Restated Credit
Agreement") which amended and restated the terms of the Original Credit
Agreement as amended by the First Amendment to Credit Agreement to (i) increase
the revolving credit from $1,500,000 to $5,000,000, (ii) add Software and
InterCon as borrowers under the revolving credit (to the extent provided
therein), (iii) increase the term credit from $8,500,000 to $13,500,000 and (iv)
make certain other changes, all as set forth in the Amended and Restated Credit
Agreement;

         WHEREAS, on April 8, l996, Software merged with and into InterCon, with
InterCon as the surviving entity;

         WHEREAS, as of August 13, 1996, PSI, InterCon and the Bank entered into
an amendment to the Amended and Restated Credit Agreement (the "First Amendment
to Amended and Restated Credit Agreement") to (i) increase the term credit from
$13,500,000 to $18,500,000, (ii) extend the Term Credit Expiration Date to June
30, 1997, and (iii) make certain other changes, all as set forth in the First
Amendment to Amended and Restated Credit Agreement.

         WHEREAS, PSI desires to sell the stock of InterCon to Ascend
Communications, Inc., a Delaware corporation, pursuant to the terms of a Stock
Acquisition Agreement (the "Sale") and the Bank is willing to consent to the
Sale subject to PSI and Pipeline executing this Agreement and agreeing to be
bound by the terms hereof.
<PAGE>
          NOW, THEREFORE, in consideration of the mutual promises contained in
this Agreement, the receipt and sufficiency of which are hereby acknowledged,
the parties hereto agree as follows:

         1. The terms "Borrower" and "Borrowers" as used in the Amended and
Restated Credit Agreement, as amended by the First Amendment to Amended and
Restated Credit Agreement and this Agreement, shall, for all purposes, from and
after the date hereof have the meaning set forth in the first paragraph of this
Agreement, and if at any time there is only a single "Borrower," references to
"Borrowers" shall be deemed to refer only to such single "Borrower"; prior to
the date hereof such terms shall have the meaning ascribed to them in the
Amended and Restated Credit Agreement. All references in the Amended and
Restated Credit Agreement to "Agreement" shall from and after the date hereof
mean the Amended and Restated Credit Agreement as amended by the First Amendment
to Amended and Restated Credit Agreement and this Agreement.

         2. Sections 1.03, 2.01, 4.15, 4.22, 4.23, 4.24, 4.25 and 4.26 of the
Amended and Restated Credit Agreement as amended by the First Amendment to
Amended and Restated Credit Agreement are hereby amended, as of the effective
date of this Agreement, by deleting said Sections in their entirety and
substituting therefore the following:

         Section 1.03.  The Revolving Credit.

         (a) Terms of the Revolving Credit. Subject to the terms and conditions
hereof and provided no Event of Default, or event which with the passage of time
or the giving of notice or both would become an Event of Default, has occurred,
the Borrowers may, jointly and severally, from time to time from the date hereof
up to June 30, 1997 (the "Revolving Credit Maturity Date") borrow and reborrow
from the Bank, and the Bank shall advance funds to the Borrowers (an "Advance"
or the "Advances"); provided that

                  (A) the aggregate of all Advances outstanding at any time
         during the term of the Revolving Credit shall not exceed the lesser at
         such time (the "Availability") of (i) the Maximum Revolving Credit, or
         (ii) an amount equal to the "Borrowing Base," each as defined below;
         and

                  (B) the aggregate of all Advances outstanding at any time
         during the Revolving Credit in favor of PSI shall not exceed the lesser
         at such time (the "PSI Availability") of (i) the Maximum Revolving
         Credit or (ii) an amount equal to the PSI Borrowing Base, each as
         defined below.

         (b) Maximum Revolving Credit and Borrowing Base. The "Maximum Revolving
Credit" at any time shall equal $5,000,000 less the aggregate undrawn face
amount of all L/Cs outstanding at such time.

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<PAGE>

         The Borrowing Base shall be equal from time to time to the sum of the
PSI Borrowing Base.

         The PSI Borrowing Base shall be equal from time to time to 75% of PSI's
Qualified Accounts less the sum of (i) 100% of the maximum outstanding liability
under any L/Cs issued pursuant to Section 1.05 of this Agreement and (ii) (A)
twenty percent (20%) of the aggregate outstanding principal amount of Term
Credit Advances made after November 10, 1995 minus (B) the amount of cash
collateral maintained by PSI at the Bank on terms satisfactory to the Bank.

         "Qualified Accounts" shall mean accounts receivable owed to a Borrower
which (a) arise from the sale of goods or the provision of services by such
Borrower (but only to the extent such goods or services have actually been
delivered or provided to the account debtor), (b) are not outstanding for more
than ninety (90) days after the original invoice date, (c) are due from an
account debtor located in the United States, (d) are subject to a perfected
first priority security interest in favor of the Bank, (e) are not represented
by a note or other negotiable instrument, (e) are not subject to any setoff,
dispute, credit, allowance or adjustment by the account debtor, and (f) have not
been deemed unsatisfactory by the Bank in the exercise of its reasonable
judgment.

         PSI shall furnish to the Bank not later than fifteen (15) days
following the end of each monthly accounting period a Borrowing Base Certificate
in the form of Exhibit 1.03(b) attached hereto, completed and signed by PSI's
chief financial officer. The Borrowing Base shown on such certificate shall be
as of the last day of said monthly accounting period. The Bank shall be under no
obligation to make any further advance if a Borrowing Base Certificate is not
delivered within the specified period.

         In calculating the Borrowing Base hereunder, there shall be excluded
from all Qualified Accounts the full amount of any deposit which an account
debtor may have paid with respect to the goods to which such account receivable
relates.

         (c) Limit on Advances Outstanding. The aggregate Advances outstanding
at any time during any monthly period shall not exceed the lesser of the
Borrowing Base or the Maximum Revolving Credit. The aggregate Advances
outstanding at any time during any monthly period in favor of PSI shall not
exceed the lesser of the PSI Borrowing Base or the Maximum Revolving Credit. If
the aggregate Advances outstanding at any time exceed the amounts set forth in
this Section 1.03(c), then the Borrowers shall forthwith pay such excess, and
the Bank may, without prior notice to the Borrowers, charge the Borrowers'
accounts with the Bank in order to effect such payment.

         (d) The Revolving Credit Note. All amounts owed by the Borrowers with
respect to Advances made by the Bank shall be evidenced by a promissory note in
the principal amount of $5,000,000 in the form attached to this Agreement as
Exhibit 1.03(d) (the "Revolving Credit Note"). The unpaid principal balance of
the Revolving Credit Note may be

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<PAGE>

voluntarily prepaid in whole or in part at any time without premium or penalty.
Payment of such excess on account of a Borrower may be made by a borrowing by
another Borrower, subject to the limits set forth in this Agreement.

         (e) Interest. Advances made by the Bank shall bear interest prior to
maturity or the occurrence of an Event of Default (computed on the basis of
actual number of days elapsed over a 360-day year) on the unpaid principal
balances outstanding from time to time at a rate per annum equal to the Prime
Rate plus one and one-half percent (1.5%). Interest shall be payable monthly in
arrears on the last day of each month commencing in the month in which the
Revolving Credit Note is issued. After maturity, or after the occurrence of an
Event of Default and until said Event of Default shall have been cured or waived
in writing by the Bank, amounts outstanding under the Revolving Credit Note
shall bear interest at the Prime Rate plus four and one-half percent (4.5%).

         (f) Requests for Advances. Subject to the terms and conditions
contained in this Agreement, each Advance shall be made on the Banking Day on
which the Bank receives notice from PSI, if such notice is received prior to
11:00 a.m. on such Banking Day, and otherwise on the next Banking Day. Each
request for an Advance shall be made to the Bank in writing or by telephone by a
duly authorized representative of PSI, and the Bank may rely upon any telephone
request which it believes is made by such a representative. Each Borrower agrees
and holds the Bank harmless for any action, including the making of Advances
hereunder, or loss or expense, taken or incurred by the Bank in good faith
reliance upon such telephone request. At the time of the initial request for an
Advance made under this Section 1.03, PSI shall have provided the Bank with a
Compliance Certificate (as defined in Section 4.07(a)). Each of the Borrowers
hereby agrees (i) that the Bank shall be entitled to rely upon the most recent
Compliance Certificate in the Bank's possession until it is superseded by
another certificate, and (ii) that each request for an Advance, whether by
telephone or in writing or otherwise, shall constitute a confirmation that the
representations and warranties contained in the most recent Compliance
Certificate then in the Bank's possession continue to be true and correct in all
respects.

         (g) Expiration. The Revolving Credit shall expire on the Revolving
Credit Maturity Date and all then outstanding Advances shall be due and payable
on such date together with all accrued and unpaid interest thereon and any other
amounts then due.

         Section 2.01.  Corporate Existence and Power.

         Each Borrower and Pipeline is a corporation duly incorporated, validly
existing and in good standing under the laws of the State of New York or
Delaware and has full corporate and other power and authority to conduct its
business and own its assets as now conducted and owned. Each Borrower is duly
licensed, qualified and authorized to do business and is in good standing as a
foreign corporation in each jurisdiction where the failure to be licensed,
qualified or authorized to do business as a foreign corporation would have a
material adverse

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<PAGE>

effect upon its business, properties, assets, prospects, operations or
condition, financial or otherwise.

         Section 4.15.  Loans and Investments.

         Except as set forth on Schedule 4.15, neither the Borrower nor any
Subsidiary will purchase or otherwise acquire or retain any stock or obligations
of, or make any loans or advances to, or investments in, any corporation or
other entity or person, other than:

            (a) obligations of the United States of America, or any agency
thereof, maturing not more than one (1) year from the date of issue thereof, or
mutual funds comprised of the same, provided that the Bank shall acquire a
perfected first-priority security interest in such obligations simultaneously
with such purchase or acquisition;

            (b) certificates of deposit or other deposit obligations maturing
not more than one (1) year from the date of issue thereof issued by any bank
within the United States of America having total combined capital and surplus in
excess of $100,000,000;

            (c) short-term investment grade debt securities;

            (d) by PSI in wholly-owned Subsidiaries, provided that the aggregate
outstanding amount of all such amounts during this Agreement shall not exceed
$22,500,000, excluding (i) any amounts previously advanced to Pipeline, it being
understood that no future amounts shall be advanced to Pipeline without the
prior written consent of the Bank, (ii) any amounts advanced to PSINet Europe
Limited, an Irish corporation, but only to the extent of advances or investments
by The Chatterjee Group in or to PSI or its Subsidiaries for that particular
purpose, and (iii) any amounts owing to PSI by its Subsidiaries as a result of
services rendered by PSI to such Subsidiaries; and

            (e) loans, advances and guarantees to employees of the Borrower and
its Subsidiaries in an aggregate amount for all of the Borrowers and their
Subsidiaries taken together not to exceed $500,000.

         Section 4.22.  Quick Assets to Funded Debt Ratio.

         As of March 31, 1997 and thereafter, the ratio of Quick Assets to
Funded Debt shall at all times equal or exceed 1.25:1.00; provided that if
Consolidated EBITDA (as defined in Section 4.24) of the Borrowers and their
Subsidiaries in any fiscal quarter is equal to or greater than $3,750,000, the
ratio of Quick Assets to Funded Debt shall thereafter equal or exceed 1:00:1.00.

         "Quick Assets" shall mean the sum of all cash, cash equivalents,
accounts receivable, short-term investments (as defined by generally accepted
accounting principles), marketable

                                       5
<PAGE>

securities (as defined by generally accepted accounting principles) of the
Borrowers and their Subsidiaries on a consolidated basis.

         "Funded Debt" shall mean all indebtedness for borrowed money of the
Borrowers and their Subsidiaries, including without limitation, the Revolving
Credit, the Term Credit and Capitalized Leases.

         Section 4.23.     Tangible Net Worth.

         The Tangible Net Worth shall as of the last day of each fiscal quarter
commencing with the fiscal quarter ending June 30, 1996 equal or exceed the sum
of $67,500,000, plus (X) 80% of all positive Net Income earned during each
fiscal quarter commencing with the fiscal quarter ended September 30, 1996, plus
(Y) 50% of the net tangible proceeds received from the sale by PSI of any shares
of its capital stock during each fiscal quarter commencing with the fiscal
quarter ended September 30, 1996.

         "Tangible Net Worth" shall mean an amount determined in accordance with
generally accepted accounting principles equal to the difference between (a) the
Stockholders' Equity of the Borrowers and their Subsidiaries on a Consolidated
basis, minus (b) the total book value of all assets of the Borrowers and their
Subsidiaries on a Consolidated basis which would be treated as intangible
assets.

         "Net Income" shall mean, with respect to any period, the net income (or
net loss) of the Borrowers and their Subsidiaries on a consolidated basis, after
deduction of all expenses, taxes and other proper charges determined in
accordance with generally accepted accounting principles; provided, that any
gain or loss resulting from an investment by the Borrower and their Subsidiaries
in any Affiliate which is not a Subsidiary shall not be included for purposes of
determining Net Income, and provided further that any gain or loss resulting
from any extraordinary or non-recurring item shall not be included for purposes
of determining Net Income.

         "Stockholders' Equity" shall mean an amount determined in accordance
with generally accepted accounting principles equal to the difference between
(a) the assets of the Borrowers and their Subsidiaries on a Consolidated basis
minus (b) the liabilities of the Borrowers and their Subsidiaries on a
Consolidated basis.

         Section 4.24.     Consolidated EBITDA.

         (a) As of the last day of the fiscal quarter ended March 31, 1997, the
Borrowers shall have Consolidated EBITDA of not less than ($7,500,000).

         (b) As of the last day of the fiscal quarter ended June 30, 1997, the
Borrowers shall have Consolidated EBITDA of not less than ($3,000,000).

                                       6
<PAGE>

         (c) As of the last day of the fiscal quarter ended September 30, 1997,
the Borrowers shall have Consolidated EBITDA of not less than $2,500,000.

         "Consolidated EBITDA" shall mean Adjusted Net Income plus to the extent
deducted in determining Adjusted Net Income, interest expense of the Borrowers
and their Subsidiaries on a consolidated basis for such period.

         "Adjusted Net Income" shall mean, with respect to any period, the total
of (a) Net Income with respect to such period, plus (b) to the extent deducted
in determining Net Income, taxes, depreciation and amortization expenses of the
Borrowers and their Subsidiaries on a consolidated basis for such period.

         Section 4.25. Leverage Ratio. The ratio of the Borrowers' and their
Subsidiaries' Total Liabilities (excluding any liabilities of the Borrowers
recorded as deferred revenue as a result of the accounting treatment by the
Borrowers of service contract revenues) on a consolidated basis to Tangible Net
Worth shall not exceed 1.25:1.00; provided that if the Consolidated EBITDA of
the Borrowers and their Subsidiaries in any fiscal quarter is equal to or
greater than $3,750,000, the ratio of Total Liabilities to Tangible Net Worth
shall thereafter not exceed 1.50:1.00.

         "Total Liabilities" shall mean all liabilities of the Borrowers and
their Subsidiaries on a consolidated basis that are treated as liabilities under
generally accepted accounting principles, including the Revolving Credit and the
Term Credit.

         Section 4.26. Debt Service Ratio. The ratio of Consolidated EBITDA to
Debt Service shall, as of the last day of each fiscal quarter commencing with
the fiscal quarter ended December 31, 1997 equal or exceed 1.00:1.00.

         "Debt Service" shall mean, with respect to any period, all payments of
principal or interest by the Borrowers and their Subsidiaries on a consolidated
basis on account of indebtedness for borrowed money including, without
limitation, payment of principal and interest on account of the Credit.

         3. Section 4.29 is hereby added to the Amended and Restated Credit
Agreement as follows:

         "Section 4.29.    Stock Acquisition Agreement Relating to InterCon.

                  The Borrowers shall deliver to the Bank executed copies of the
         Stock Acquisition Agreement and all material documents, instruments and
         agreements executed in connection therewith."

         4. The Bank hereby consents to the Sale for all purposes under the
Amended and Restated Credit Agreement, as amended. Simultaneously with the
Closing (as defined under

                                       7
<PAGE>

the Stock Acquisition Agreement), the Bank agrees to execute and deliver to the
Borrower all documents reasonably necessary to release its liens on the assets
of Software and InterCon and to release all obligations of InterCon and Software
to the Bank, including without limitation, all guaranties.

         5. Schedules 2.02 and 2.17 to the Amended and Restated Credit
Agreement, as amended by the First Amendment to Amended and Restated Credit
Agreement, are hereby amended as provided on Schedule I attached hereto
effective upon Closing (as defined in the Stock Acquisition Agreement).

         6. After giving effect to this Agreement, all representations and
warranties made by the Borrowers in the Amended and Restated Credit Agreement
and the Security Documents are true and correct as of the date hereof, except
for those representations which relate to a specific date which are true and
correct as of such date.

         7. The Borrowers represent, on behalf of themselves and each of their
Subsidiaries, that they have performed and complied with all covenants and
agreements required to be performed and complied with by them under the Amended
and Restated Credit Agreement as amended by the First Amendment to Amended and
Restated Credit Agreement and this Agreement and the Security Documents as
amended by the First Amendment to Amended and Restated Credit Agreement and this
Agreement except to the extent performance or compliance has been waived in
writing by the Bank.

         8. Except as amended by the First Amendment to Amended and Restated
Credit Agreement and this Agreement and any other written agreements of the
Bank, all provisions of the Amended and Restated Credit Agreement, the Security
Documents and all other documents referred to therein shall remain in full force
and effect after giving effect to this Agreement.

         9. The amendments set forth in this Agreement shall not be effective,
and the Bank shall not be obligated to amend, modify or alter the Amended and
Restated Credit Agreement unless and until all of the following conditions shall
have been fulfilled or waived by the Bank:

            (a) Closing. The Closing (as defined in the Stock Acquisition
Agreement) shall have taken place and the Borrower shall have received the
consideration provided for therein.

            (b) Fee. The Bank shall have received from the Borrowers a fee of
$50,000 in connection with this Second Amendment to Amended and Restated Credit
Agreement.

         10. This Agreement represents the entire agreement among the parties
thereto relating to the amendment to the Amended and Restated Credit Agreement
effected hereby, and supersedes all prior understandings and agreements among
the parties relating to the subject matter of this amendment to the Amended and
Restated Credit Agreement.

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<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement
under seal as of the date first above written.

                                            PSINET INC.

                                            By:   /s/ William L. Schrader
                                                  ------------------------------
                                                  Name:  William L. Schrader
                                                  Title: President & CEO

                                            PSINET PIPELINE NEW YORK, INC.*

                                            By:   /s/ William L. Schrader
                                                  ------------------------------
                                                  Name:  William L. Schrader
                                                  Title: President & CEO

                                            FLEET NATIONAL BANK

                                            By:   /s/ Thomas W. Davies
                                                  ------------------------------
                                                  Name:  Thomas W. Davies
                                                  Title:  Vice President

*PSINet Pipeline New York, Inc. executes this Agreement for the sole purpose of
acknowledging and confirming that the Obligations under the Security Documents
shall be deemed to include any additional Obligations created by this Agreement.


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