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                                 REVOLVING NOTE


$3,500,000                                                        April 23, 1998
                                                                McLean, Virginia

      FOR VALUE RECEIVED, ACE*COMM CORPORATION, a Maryland corporation (the
Borrower), hereby promises to pay to the order of CRESTAR BANK, a Virginia
banking corporation (the Lender), at Commercial Loan Services, P.O. Box 26202,
Richmond, Virginia 23260-6202, or such other location as the holder hereof may
in writing designate, the principal sum of THREE MILLION FIVE HUNDRED THOUSAND
AND NO/100 DOLLARS ($3,500,000) (or such lesser amount as shall equal the
aggregate unpaid principal amount of the Loans made by the Lender to the
Borrower under the Loan Agreement described below), in lawful money of the
United States of America in immediately available funds, on demand, without
defense, offset or counterclaim, and to pay interest on the unpaid principal
amount of the Loans, at such office, in like money and funds, for the period
commencing on the date of each Loan until such Loan shall be paid in full, at
the rate per annum and on the dates provided in the Loan Agreement. The Borrower
may borrow, prepay without penalty, and reborrow hereunder in accordance with
the provisions of the Loan Agreement.

      The Lender is hereby authorized by the Borrower to maintain records of the
amount of each Loan made by the Lender, the date such Loan is made, and the
amount of each payment or prepayment of principal of such Loan received by the
Lender. The Borrower agrees that the amounts so evidenced in such records,
absent manifest error, shall constitute conclusive evidence of the amount owed
hereunder.

      This Revolving Note is the Revolving Note referred to in the Loan and
Security Agreement (as amended, modified or supplemented from time to time, the
Loan Agreement), of even date herewith, between the Borrower and the Lender, and
evidences Loans made by the Lender thereunder. Capitalized terms used in this
Revolving Note have the respective meanings assigned to them in the Loan
Agreement.

      Upon the occurrence and continuation of an Event of Default, the principal
hereof and accrued interest hereon may be declared to be, or may become,
forthwith due and payable in the manner, upon the conditions and with the effect
provided in the Loan Agreement.

      The Borrower, every guarantor and endorser hereof hereby waive
presentment, demand, notice of dishonor, protest and all other demands and
notices in connection with the delivery, acceptance, performance and enforcement
of this Revolving Note.

      Upon the occurrence of an Event of Default, the Borrower hereby authorizes
any attorney designated by the Lender or any Clerk of any court of record to
appear for the Borrower in any court of record and to confess judgment without
prior hearing against the Borrower in favor of 

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the Lender for and in the amount of the unpaid principal balance hereof, all
interest accrued and unpaid thereon, all other amounts payable by the Borrower
to the Lender under the terms of this Note or any of the other Loan Documents,
costs of suit, and attorneys' fees of $7,500 (if judgment be entered without
contest). If confession of judgment is contested, attorneys' fees under this
paragraph shall be ten percent (10%) of the unpaid principal balance hereof and
interest then due hereunder. The Borrower hereby releases, to the extent
permitted by applicable law, all errors and all rights of exemption, appeal,
stay of execution, inquisition, and other rights to which the Borrower may
otherwise be entitled under the laws of the United States of America or of any
state or possession of the United States of America now in force or which may
hereafter be enacted. The authority and power to appear for and enter judgment
against the Borrower shall not be exhausted by one or more exercises thereof or
by any imperfect exercise thereof and shall not be extinguished by any judgment
entered pursuant thereto. Such authority may be exercised on one or more
occasions or from time to time in the same or different jurisdictions as often
as the Lender shall deem necessary or desirable, for all of which this Note
shall be a sufficient warrant. Notwithstanding any provision of this paragraph,
the Borrower retains its rights pursuant to Maryland Rules of Civil Procedure
Rule 2-611.

      This Revolving Note shall be governed by and construed in accordance with
the laws of the State of Maryland, without reference to conflict of laws
principles.

      IN WITNESS WHEREOF, the Borrower has caused this Revolving Note to be
executed by its duly authorized representative as of the day and year first
above written.


                                    BORROWER:     

                                    ACE*COMM CORPORATION,
                                    a Maryland corporation


                                    By: 
                                        --------------------------------
                                    Name:
                                         -------------------------------
                                    Title:
                                          ------------------------------


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