What's with so many people loving mtgox? they have "some responsibility" for writing crappy software, getting hacked via a dodgy auditor and getting the entire contents of the exchange sold off in 5 minutes? You're right, they do have the tiniest smidgeon of responsibility there...
The person whose account was hacked (if it was one person) is entitled to their Bitcoins and it's MtGox's responsibility to provide that to him. Kevin did nothing wrong making a large purchase of bitcoins, but now that he KNOWs the bitcoins were stolen, he's possessing stolen property, which can be a felony. The fact that MtGox's account was hacked makes all the difference here, as it makes the bitcoins which were traded stolen property.
If Kevin wanted, and as I'm sure a few other people have done, he could have purchased those coins, withdrawn every single one of them by exploiting the bug he identified, and then stayed quiet. Kevin, who is doing the right thing, will have 250k coins taken off him in the rollback, and would probably return those 600 coins if asked, other shadier people will have got away with some money, will stay quiet about it, and will get to keep it.
I think we're rewarding the wrong people here!