I've always considered virus writers to be incredibly skilled. Not the type that take advantage of hole in the OS, but those who used to do the real nasty ones.
I remember the news of the Razor1911 "leader" getting arrested for fraud/theft of over £300,000 worth of Cisco equipment. He was a con-man and posed as a journalist for various magazines, which is how he got the equipment and games to "review" and would then copy/crack/release the games, and just not give the equipment back and either use it or sell it.
Don't forget, certain people who are "close" to the games companies will get given the source code.
Now if that code was to find it's way onto a public domain - well it would be pretty simple to just remove the copy protection.
Although I don't understand virus makes at all. Why would you intentionally wreck someone else's computer? It's not like it makes them famous as a result. They just strike me as sad, lonely little people with a severe bitterness complex.