A bit more on the whole cheating issue, the guys on /. carried a story today about the earlier .plan update from John Carmack on cheating with the Quake1 source release. Well Carmack has a quick comment here which basically states the obvious to programmers but may interest a few of you guys on the slow-slow weekend: (Thanks King_Darius)

There are server-side countermeasures that look for sequences of moves that are likely to be bot-generated and not human-generated, but that is an arms race that will end with skilled human players eventually getting identified as subtle bots.

Media cheats can be protected by various checksums, as we do in Q3 with the sv_pure option. This is only effective if the network protocol is not compromised, because otherwise a proxy can tell the client that it's hacked media are actually ok.

If the network protocol is not known, then the extra-information cheats generally can't happen unless you can hack the client source.