Summary

The 'W95/PennyTools.Trojan' or 'Trojan.Aol.Buddy' is an AOL password stealing trojan. Three versions are currently known (by May 1999). One version was spread inside MS Word document advertising access to AOL for free. If a user clicks on AOL logo in the document his system becomes infected. Another version is spread in another word document that has only setup icon.

This trojan uses a tricky way of installing itself to system. It uses 5 different ways at the same time to make disinfection more difficult:

1. Through Registry by modifying RUN key to launch C:\COMMAND.EXE

   hidden file which is a trojan's body

2. Through SYSTEM.INI by adding a screensaver reference routine

   to C:\Windows\System\WINSAVER.EXE - the system will become
   infected when screen saver starts.

3. Through WIN.INI - by adding to execution of C:\America Online

   4.0\BUDDYLIST.EXE hidden file to LOAD= string with more than
   80 spaces in front of line to hide it

4. Again through WIN.INI - by adding to execution of

   C:\Windows\System\NortonAntiVir\REGISTRYREMINDER.EXE hidden
   file to RUN= string

5. Through Windows startup directory - by placing AIM

   REMINDER.EXE file in \Windows\Start Menu\Programs\Startup\
   folder.

Also a DLL is created in Windows\System folder with the name VCLCNTL.DLL but it contains some text data for the trojan, not DLL code. When Windows is started the trojan is also started (one of steps 1-5) and remains active during all Windows session. It sends user's AOL login and password as e-mail to qware4019@hotmail.com, ha015312@hotmail.com or liighthack@yahoo.com addresses (depending on trojan version).

To disinfect the trojan manually a user should exit to DOS and manually remove all five trojan files from locations specified above. As trojan files and directories have hidden attribute the ATTRIB utility should be used before deleting to make files and directories 'visible'.

[Analysis: Alexey Podrezov, F-Secure]