<PAGE>
                                                                   EXHIBIT 10.23


                                    ANNEX K

                     Third Amendment to the Agreement and
                   Plan of Merger by and Among Halis, Inc.,
              HealthWatch Merger Sub, Inc. and HealthWatch, Inc.
                         dated as of January 16, 2001


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                            THIRD AMENDMENT TO THE
                            ----------------------
  AGREEMENT AND PLAN OF MERGER BY AND AMONG, HALIS, INC., HEALTHWATCH MERGER
  --------------------------------------------------------------------------
                        SUB, INC. AND HEALTHWATCH, INC.
                        -------------------------------


     This THIRD AMENDMENT TO THE AGREEMENT AND PLAN OF MERGER BY AND AMONG,
HALIS, INC., HEALTHWATCH MERGER SUB, INC. AND HEALTHWATCH, INC. ("Amendment"),
dated as of February 16, 2001 is made and entered into by and among (i) Halis,
Inc. ("Halis"), a Georgia corporation, (ii) HealthWatch Merger Sub, Inc.("Merger
Sub"), a Georgia Corporation  and (iii) HealthWatch, Inc. ("HealthWatch"), a
Minnesota corporation.

     WHEREAS, Halis, Merger Sub and HealthWatch have entered into that certain
Agreement and Plan of Merger dated as of June 29, 2000, as amended by the
parties on September 29, 2000 and January 31, 2001 (the "Agreement"), in which
HealthWatch will acquire Halis upon the merger of Halis with and into Merger
Sub, a wholly-owned subsidiary of HealthWatch, upon the terms and conditions
included in the Agreement; and

     WHEREAS, the parties desire to extend the lock-up period provided in
Section 5.13  of the Agreement to allow the parties the benefits of the lock-up
provision as contemplated by the parties when the Agreement was first executed
on June 29, 2000.

     THEREFORE, for good and valuable consideration, the receipt and sufficiency
of which hereby are acknowledged, the parties, intending to be legally bound, do
hereby agree as follows:

     1.   Section 5.13 of the Agreement shall be deleted in its entirety and
replaced with the following:

     "SECTION 5.13 LOCK-UP.   Substantial Halis Stockholders (defined as
     directors, officers and Halis Shareholders owning 5% or more of Halis
     Common Stock) and Affiliates will be required to agree not to sell,
     transfer or otherwise dispose of any HealthWatch Common Stock prior to
     December 31, 2001 (the "Lockup Period"); if HealthWatch undertakes a public
     offering within the Lockup Period, Halis Stockholders shall agree not to
     sell, transfer or otherwise dispose of the HealthWatch Common Stock for
     such period of time after completion of such public offering (not to exceed
     one year).  In addition, Halis shall use its best efforts to obtain similar
     lock-up agreements from other Halis Shareholders that the parties shall
     reasonably determine to be in the best interest of all of the parties in
     carrying out the transactions contemplated by this Agreement.

     2.   Except as modified by this Amendment, all terms and conditions of the
Agreement are hereby reaffirmed.
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     IN WITNESS WHEREOF, the undersigned have executed this Amendment as of the
effective date mentioned above.

                                         HALIS, INC.

                                           By:  /s/ Joel Greenspan
                                                ------------------------------
                                           Its: Director
                                                ------------------------------
                                           Attest: /s/ Marilyn May
                                                   ---------------------------
                                           Its: Asst. Secretary
                                                ------------------------------

                                                      [CORPORATE SEAL]

                                           HEALTHWATCH, INC.

                                           HEALTHWATCH MERGER SUB, INC.

                                           By:  /s/ Thomas C. Riderour
                                                -----------------------------
                                           Its: Chief Financial Officer
                                                -----------------------------

                                           Attest: /s/ Marilyn May
                                                   --------------------------
                                           Its: Asst. Secretary
                                                -----------------------------

                                                      [CORPORATE SEAL]

                                           By:  /s/ Paul W. Harrison
                                                ------------------------------
                                           Its: President
                                                ------------------------------

                                           Attest: /s/ Marilyn May
                                                   ---------------------------
                                           Its: Asst. Secretary
                                                ------------------------------

                                                      [CORPORATE SEAL]

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