Summary

S-Bug is a highly polymorphic virus that has been reported to be in the wild in USA and in several other locations.

Virus stays resident in memory occupying 9 KB's of DOS memory. It hooks the following INT 21h functions: 3Dh, 4Bh, and 6Ch. Infected files grow in size between 4k and 5k bytes.

Infected EXE and overlay files may fail to execute correctly. Virus includes string "Satan Bug virus - Little Loc".

The virus will only become resident if the environment variable COMSPEC= is set to point to a file called COMMAND.COM.

S-Bug virus also removes validation codes added to files by McAfee SCAN and CPAV's Immunize function.

Additional Details

VARIANT:

FruitFly

A related variant. Uses similar encryption, but the actual virus is simpler and non-resident.

See: Natas

[Analysis: Mikko Hypponen, F-Secure]