Virus Name: 981
Aliases: Joe's Demise
V Status: Rare
Discovery: May, 1992
Symptoms: .COM & .EXE file growth; decrease in total system and
available free memory
Eff Length: 981 - 1,932 Bytes
Type Code: PRhA - Parasitic Resident COM & .EXE Infector
Detection Method: ViruScan, AVTK, Sweep, F-Prot, IBMAV, NAV,
NAVDX, VAlert, PCScan, ChAV,
NShld, Sweep/N, LProt, Innoc, NProt, AVTK/N, IBMAV/N,
Removal Instructions: Delete infected files
The 981 virus was discovered in the United States in May, 1992. Its
origin is unknown. This virus is a memory resident infector of
.COM and .EXE files, but not COMMAND.COM.
When the first 981 infected program is executed, the 981 virus will
install itself memory resident at the top of system memory but
below the 640K DOS boundary. Interrupt 12's return will not be
moved. Total system and available free memory, as indicated by the
DOS CHKDSK program, will have decreased by 1,952 bytes. Interrupts
21 and 22 will be hooked by the virus in memory.
Once memory resident, the 981 virus will infect .COM and .EXE
programs when they are executed or opened for any reason. .COM
files increase in size by 981 bytes, though if the file was
originally smaller than 981 bytes, they will become 1,934 bytes in
length. .EXE files increase in size by 1,015 to 1,025 bytes. In
both cases the virus will be located at the end of the program.
This virus will sometimes reinfect previously infected programs,
adding an additional 981 bytes to the file. The infected program's
date and time in the DOS disk directory listing will not be
One text string can be found in all 981 infected programs:
"This program requires MS-DOS 3.00 or later"
It is unknown what the 981 virus may do besides replicate.
Known variant(s) of 981 are:
Joe's Demise: Functionally similar to the original virus, this
variant has 11 bytes which differ.
Origin: Unknown June, 1992.