Whenever your anti-virus program fails or you are having to clean someone else's computer, a way to clean your system is by using malware scanners. If you ever have the need for these types of tools, one you should take a look at it is a-squared Free.Like most tools in it's class, a-squared Free scans for the typical set of malware and cleans it appropriately. For the most part, scanners are better at detecting certain types of malware than others which means you can never have too many (within reason of course). One nice feature about a-squared is it designed to run along side other anti-virus programs without causing problems.Again, cleaning a badly infected system can be a big chore so the more tools you have available, the better.