Thirty Three Virus

Virus Name: Thirty Three Aliases: V Status: New Discovered: November, 1993 Symptoms: .COM file growth; file date/time changes; decrease in total system & available free memory Origin: Unknown Eff Length: 525 Bytes Type Code: PRtCK - Parasitic Resident .COM Infector Detection Method: IBMAV, F-Prot, ViruScan, AVTK, Sweep, ChAV, NAV, NAVDX, VAlert, Sweep/N, NShld, AVTK/N, IBMAV/N, Innoc, NProt, NAV/N Removal Instructions: Delete infected files General Comments: The Thirty Three virus was received in November, 1993. Its origin or point of isolation is unknown. Thirty Three is a memory resident infector of .COM programs, including COMMAND.COM. When the first Thirty Three infected program is executed, this virus will install itself memory resident at the top of system memory but below the 640K DOS boundary, moving interrupt 12's return. Total system and available free memory, as indicated by the DOS CHKDSK program, will have decreased by 1,024 bytes. Interrupt 21 will be hooked by the virus in memory. Once memory resident, the Thirty Three virus will infect .COM programs when they are executed. Infected programs will have a file length increase of 525 bytes with the virus being located at the end of the file. The program's date and time in the DOS disk directory listing will have been updated to the current system date and time when infection occurred. One text string is visible within the viral code: "33" It is located very near the end of all infected files.