It is illegal. Actually, in most of Europe unauthorized access to computer system is a criminal offense that might lead to jailtime, while downloading pirate movie/game is a small wrongdoing that nets you fine (unless it's for profit, large scale operation). And that's access only, distributing malware and stealing personal data are two more, separate criminal offenses. So basically that's shooting a boy who has tried to steal an apple in a crowded market.

Exactly my thought - this sounds like a criminal matter, not a civil one.

It's the same reason you don't try to brick someone's computer even if you can prove with certainty that they were, say, cheating and griefing on your game's multiplayer. None of that matters, it would still be a crime.

In which country are these guys based?