People being hacked since the last Server Check.

Id's aren't random. All you'd need to do is understand how the packet in question related to the account it brought back and extrapolate it to use on other characters by simple incrementation and guesswork. Tedious, but going account by account will eventually strike it rich.

Going by that, I would assume that this sort of method would not be very widespread, as it would require a fair amount of technical knowledge to operate. Furthermore, like you said, it would be difficult to target a specific account, and far easier to simply hit random ones.

Since most of the account hackings (or at least the ones we hear about) seem to target big fish, I'd say this packet method isn't the main way people are being hacked.

Either way, I'm quite alarmed that this kind of security hole exists... it's pretty inexcusable for a game of this magnitude. All goes back to the very poorly designed server/client relationship.