Threat Encyclopedia

Selected viruses, spyware, and other threats: sorted alphabetically

33

The virus 33 is a resident parasitic COM infector 525 bytes long. It reserves 1KB of memory for its own use. It infects itself in such a way that after calling DOS service FFFFh it expects the number 3333h. One can recognize the infected files by the string ”33“ present before the last file byte After the virus is executed 10th time it resets the computer. Programs are infected either when they are started or when DOS services Find First and Find Next is called. This may cause a relatively fast spreading of the virus in system. When infecting a potential victim the virus checks whether it does not have EXE file structure. But it checks the length incorrectly and that is why it damages very long files of COM type. The virus does not recognize write protection of diskettes and it discloses its presence by a standard message about an attempt to write on a protected diskette. The most interesting thing is the “stealth and anti-debug” procedure. It causes that some heuristic cleaners do not clean the file properly.

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