Type File virus
Date Discovered JAN-1992
Place of Origin Poland
Source Language
Platform DOS
File Type(s) .com
Infection Length 1,233 bytes
Reported Costs

Checksum or CkSum is a family of viruses originating from Poland in 1992.

When an infected file is executed, Checksum installs itself at the top of system memory below the 640K DOS boundary. CHKDSK will report it is taking up 1,264 bytes in memory. The virus infects .com files as they are executed, including COMMAND.COM. The file size will increase by 1,233 bytes, and the virus will be located at the end of the file. Checksum does not change the file's time and date. Infected systems may experience frequent hangs, often when the virus infects a program or runs an infected one.


Most variants originate from Poland like the original and don't differ much from the original, all appearing at various points in 1992. Checksum.1569 can also infect .exe files. Infected .exe files often don't execute properly and return a "Divide overflow" error. Its point of origin is not as certain as the others, but it is also likelty from Poland.


Online VSUM, CheckSum Virus.

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