Like any other popular online shooter, Killzone 2 has its share of cheaters. And, like many other popular online shooters, the developers are prepared to take drastic steps to stop said cheating.
Developers Guerilla Games have issued a curt, ominous statement on the matter, which reads:
Glitchers risk losing their PSN ID altogether. We've been quite lenient so far but that's going to change.
OK, so it's not that ominous. Because there's no money involved, a PSN ID isn't as valuable as, say, an Xbox Live one (though, as some have pointed out in comments, they'd probably lose any and all downloaded content as well). Then again, if you're keen enough to cheat, you're probably self-centred enough to care about your trophies, so hopefully the threat carries weight with some of the no-do-gooders.