How to use an extra virus cleaner

Adapted from...
Important notes when scanning with an Virus Cleaner

1. During the scanning process, it is highly recommended not to start any applications.
   As already pointed out, some worms will start automatically when any other  application is started. Running worm processes are terminated/deactivated only during the first phase of the virus cleaner scanning; if you activate the worm again in the middle of the scanning process (by starting another application, such as Notepad, Explorer, ...), the worm will probably not be removed from your computer!
2. Turn off any resident (on-access) antivirus protection before running  a virus cleaner.
   The virus cleaner has to access the infected files to be able to identify and remove them. The resident protection, however, might not permit it - and the worm could not be removed from your computer! Do not forget to activate the resident protection again after the virus cleaner has finished the disinfection.
3. To work correctly, the virus cleaner requires administrator privileges when running on Windows NT/2000/XP/2003 operating systems. On an infected computer, however, it might not be wise to log in as a privileged user (administrator) - it may help the worm to spread even further.
   Therefore, you can start some virus cleaner (e.g. avast! Virus Cleaner) as a restricted user and enter the administrator login name and password directly into an avast! Virus Cleaner dialog; in such a case, the Cleaner will be run with the privileged user access rights - however, the privileged user will not be actually logged on, and none of his/her startup files will be processed.

Solving other problems
If you have deleted a virus or worm file associated to a vital file type - and now you cannot run your applications anymore, the virus cleaner may help you as well. All you have to do is run avast! Virus Cleaner "somehow". If, for example, only the association for .EXE files has been corrupted, you may run the avast! Virus Cleaner by renaming it to a .COM file. The other extensions you may try are .SCR, .BAT, .PIF (on Windows NT/2000/XP/2003, you may try .CMD as well). If none of these extensions works (Windows is still reporting "Cannot find 'xyz.exe'"
when you try to start the tool), you can use avast! The Virus Cleaner itself as a replacement for the missing file. However, you have to know the name of the missing file to do that; if you know it, just rename the avast! Virus Cleaner file to the missing name (and move it to the corresponding folder, if necessary).