Here is a thread that is showing you what happens when you do get a virus with a wallet stealer.
It plants copy and paste of someone's wallet address so when you think your sending to you address or another's you are sending it to the scammer's btc address.
http://bitcointalk.org/index.php?topic=1794944

This is just a taste of what they can do.
It gets worst mister trust me it gets much worst than this invention from 'script kiddies' just messing with their mum's computer.