F-Secure Virus Descriptions : Shell

NAME:	Shell
ALIAS:	Tentacle_II
SIZE:	10634

This virus was found in the wild in June 1996 in USA, UK, Australia, Norway and New Zealand. It has possibly been distributed over the internet several times. A known infection happened on the 3rd of August, 1996, when an infected screen saver called PCTRSHOW.ZIP was posted to the following newsgroups:

  alt.sex.pictures
  alt.binaries.pictures.erotica
  alt.binaries.pictures.erotica.blondes
  alt.binaries.pictures.erotica.breasts
  alt.binaries.pictures.erotica.cheerleaders
  alt.binaries.pictures.erotica.female
  alt.binaries.pictures.erotica.lesbians
  alt.binaries.pictures.erotica.oral
  alt.binaries.pictures.erotica.orientals
  alt.binaries.pictures.erotica.redheads
  alt.binaries.pictures.erotica.teen
  alt.binaries.pictures.erotica.teen.female
  alt.binaries.pictures.erotica.voyeurism
  alt.binaries.pictures.erotica.young
  alt.binaries.pictures.groupsex
  alt.binaries.pictures.erotica.latina
  alt.binaries.pictures.celebrities
  alt.binaries.pictures.girls

Do note that there are also clean copies of PCTRSHOW in circulation.

The virus infect only Windows 3.x executables (NE), and it does it without changing the executable entry point. This is an unusual infection method and was first introduced in this virus.

When executed, Shell.10634 searches the directory tree for suitable files to infect. Only EXE and SCR (screen saver) files can get infected.

Also 32bit Win95 and WinNT executables can be infected by the virus, but these files are unable to spread the infection further. Shell not stay resident in memory.

This virus activates by dropping a GIF file, which contains a picture of a Tentacle and text:

    I'm the Tentacle Virus!

The author of this virus also wrote the Tentacle and Tentatrickle viruses, which are technically quite different from this virus. See: Tentacle

[Analysis: Mikko Hypponen, F-Secure]