MDS Virus

Virus Name: MDS Aliases: MDS.331 V Status: New Discovered: January, 1996 Symptoms: .COM file growth; file date/time changes; decrease in available free memory Origin: Unknown Eff Length: 331 Bytes Type Code: PRhCK - Parasitic Resident .COM Infector Detection Method: ChAV, F-Prot, AVTK, IBMAV, NAV, NAVDX, ViruScan 2.54+, Innoc, AVTK/N, IBMAV/N, NAV/N, NShld 2.33+ Removal Instructions: Delete infected files General Comments: The MDS or MDS.331 virus was received in January, 1996. Its origin or point of isolation is unknown. MDS is a memory resident infector of .COM files, including COMMAND.COM. When a program infected with the MDS virus is executed, this virus will install itself memory resident at the top of system memory but below the 640K DOS boundary, not moving interrupt 12's return. Available free memory, as indicated by the DOS CHKDSK program from DOS 5.0, will have decreased by 2,048 bytes. Interrupt 21 will be hooked by the virus in memory. Once the MDS virus is memory resident, it will infect .COM files, including COMMAND.COM, when they are executed. Infected .COM files will have a file length increase of 331 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. The following text string can be found within the viral code in all infected files: "MDS93"