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====== Computer Virus Catalog 1.2: "dBase" Virus (15-Feb-1990) =======
Entry...............: "dBase" Virus
Alias(es)...........: ---
Virus Strain........: ---
Virus detected when.: October 1989
              where.: ---
Classification......: Link - Virus (extending), RAM - resident
Length of Virus.....: .COM - Files: Program length increases
                             by 1864 bytes
--------------------- Preconditions ----------------------------------
Operating System(s).: MS-DOS
Version/Release.....: 2.xx upward
Computer model(s)...: IBM - PC, XT, AT and compatibles
--------------------- Attributes ------------------------------------
Easy Identification.: Typical text in Virus body (readable with
                      HexDump-utilities): "c:\bugs.dat"
Type of infection...: System: RAM-resident, infected if function
                              FB0AH of INT 21H returns with 0AFBH
                              in AX register.
                      .COM file: extended by using EXEC-function.
                              A file will only be infected once.
                      .EXE File: no infection.
Infection Trigger...: When function 4B00H of INT 21H (EXEC) is called.
Interrupts hooked...: INT 21H
Damage..............: Permanent Damage:
                      1. Every time a .DBF file is created in an
                              infected system with function 3CH, 5BH
                              or 6CH of INT 21H, the complete filename
                              of the new .DBF file will be inserted in
                              the hidden file "c:\bugs.dat".

                      2. On every write operation to a file
                              registered in "bugs.dat", all
                              neighboring bytes will be interchanged
                              (e.g.: "01 02 03 04" changed to "02 01
                              04 03").

                      3. On every read operation from a file regis-
                              tered in "bugs.dat", the bytes will be
                              interchanged again, so that no modifi-
                              cation is visible.

                      4. If the filename of the .DBF file is
                              modified, so that it does not correspond
                              to the filename registered in
                              "bugs.dat", or read/write operations
                              happen in a non- infected system, the
                              bytes will no longer be modified by the
                              virus and they appear defective.

                      Transient Damage:
                             Every time a new .DBF file is created,
                             the virus examines the age of "bugs.dat".
                             If the difference between the month of
                             creation and the current month is greater
                             than 2, the computer will hang in an end-
                             less loop.

Particularities.....: - In case of a program error in the virus,
                        single bytes in the .DBF file could be over-
                        written incorrectly by write operations!
                      - Programs longer than 63415 bytes are no longer
                        loadable.

Special remark......: The original virus contains code which erases
                        (INT 21)  the infected DBF file structure
                        after a certain time; Ross Greenberg who
                        detec- ted this virus patched the essential
                        instruc- tion with INT 03 such that the
                        destructive part does no longer work; the rest
                        of the code was not changed.  Unfortunately,
                        the changed code escaped one virus expert's
                        computer.

------------------ Agents -------------------------------------------

Countermeasures.....: Category 3: ANTI_DBS.EXE (VTC Hamburg)
- ditto - successful: ANTI_DBS.EXE finds and restores infected
                      programs (only for DBASE).
Standard means......: Notice .COM file length.
                      Typical text in virus body: "c:\bugs.dat",
                        which is also created in the root directory.
------------------- Acknowledgement --------------------------------

Location............: Virus Test Center, University Hamburg, FRG
Classification by...: Thomas Lippke
Documentation by....: Thomas Lippke
Date................: January 20, 1990


===================== End of "DBase"-Virus ===========================


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