Resolving Virus Infections

   Last weekend my friend called me over to check his pc.His troubles started when he plugged a pen drive to his pc.Soon things took a turn for the worse;he did a scan using his anti-virus software.That resulted in a total of some 200 viruses being deleted from his system.
   This was regular;the only thing different was that there was no data in any of the drives.Hearing this I had a feeling that maybe his data were hidden by a virus.I told him to restore all settings and folders using smart virus remover.This worked..
   Another thing was when he opened my computer or any of the drives a message from some software popped up saying 'the feature you're trying to access is on a disk,insert the cd-rom and install'.Thinking it was some virus I asked him to scan again.
   Then I tried scanning using different anti-virus and anti-malware software.Alongwith this I opened task manager to see which process was causing the message.To my surprise it was the explorer process.That got me thinking maybe the process was corrupted and left me perplexed.
   Something clicked and the next thing I was in google searching for a solution.Here I got to know that message was related to the printing software.I felt that maybe the installed software had got corrupted.
  That turned out to be true;the data had been deleted but an entry was present in the Add/Remove programs folder.I removed this entry and restarted the pc;to my relief that solved the issue.
  However there was one issue I could nothing do about;during startup a strange message appeared..