Virus Database

BackFormat.1855

Description BackFormat.1855

These are dangerous memory resident parasitic viruses. "BackFormat.2354," are encrypted ones. Upon execution, they hit the COMMAND.COM file, and the length of the COMMAND.COM file doesn't increase. This virus uses the "Lehigh" virus algorithm. Then they hook INT 21h, ("BackFormat.2000" hooks INT 13h also), and write themselves to the end of COM- and EXE-files. They infect newly created files on a floppy only and write themselves upon file closing. Upon infection of a COM-file, the virus checks the first instruction of it. If this instruction is not JMP (E9h), the virus infects the file in a standard manner: it writes itself to the end of the file and overwrites the beginning of the file with a "JMP Virus" instruction. If the first byte is JMP, the virus overwrites the instruction to where the first JMP points.
These viruses contain the internal text string ":command.com".
"BackFormat.2000" depending upon generation number and system date, this version changes the system tables upon floppy disk formatting. The sectors are formatted in reverse order: from the 9th to the first (for 360k floppies). If this floppy is not 360K, the disk will not be accessible.
"BackFormat.2435" sometimes corrupts data upon it being saved on a disk.

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Parity.a

Description Parity.a

This is a dangerous memory-resident boot virus. It hooks INT 9, 13h and infects floppy boot sectors and hard drive MBR on reading from these sectors. By using INT 9 (keyboard) this virus hooks warm reboot (Alt-Ctrl-Del) and calls INT 19h (reboot). Sometimes this virus decrypts and types the message "PARITY CHECK" and then hangs up the computer.

ParityError Family

Description ParityError Family

These are very dangerous nonmemory resident parasitic viruses. They search for .COM files of the current directory, then write themselves to the end of the file. They contain the text "*.COM". They display the messages:
Water detected in math-co-processor
PARITY ERROR System halted
Something wonderful has happened, your PC is aliveall

and erase the disk sectors.

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