Well, there are many, many ways to modify a virus so it bypasses current definitions, and of course, many types of binders to do so.

The biggest risks are .wmv and .wma files, as for some stupid reason, Windows media play decided to let their files have certian background rights, like installing 'codecs' silently. The thing is, what hackers put into the codec needed portion is simply a pointer to a website with their virus.

And, I'll be honest, I'm sure not everyone that says they were hacked was actually hacked. Think of how many account trading/buying sites are out there. And they're not out there because people don't do it. So, say Joe sells his account, then either regrets it or something more malicious, goes onto the forums and claims he was hacked. Since he'll be able to answer all the right questions, he'll (usually) be able to get his account back.

No I don't really believe anyone on this site would do something like that, as we already get enough 'publicity' in game, but I do know a little bit about human nature, and a great portion of the populus wouldn't think that Blizzard owned their account when they were the ones paying for it for however long.