If you use torrent or P2P file swapping, let me introduce you to Virut
. Chances are you will soon meet on your computer if you continue to file swap.
It is being passed around rapidly now in many of the usual malware download methods, of which torrent downloading is the number one method. Regardless of what most of the AV companies seem to indicate about their ability to clean a Virut infected system, as the current variant includes tough rootkit and other malware methods it usually means game over. Reformat and reinstall time. Virut alters most system files, and also is now corrupting those so they are no longer cleanable after.
If you use torrent software, do not do any other secure transactions on the same computer, and be sure to keep a current backup of personal files available for after a reinstall. As this variant apparently offloads a list of all email addresses, torrent users should also, in all reality, warn all their friends and family that their practices may be putting their privacy at risk. This is not some silly scare tactic - Virut infections are the current plague of torrent users. Security forums like MalwareCrypt are getting more and more requests each day, and the solutions are always the same - reformat and reinstall.
If you actually download cracks you WILL
get a Virut infection - your choice.