My client and his wife were into a role-playing game, I think Second Life’? Everyone had an avatar (I suspect that his and his wife’s were much more spritely than they were in real life).

Anyway he suspected that she was being unfaithful to him in the game, so he created a fake avatar and stalked her in the game. Sure enough, she was running around on him, having virtual sex with another bloke (or bloke avatar anyway). That was it.