How does it work?

The speed cheat works by the client lying to the server about how much time has passed since the last packet was sent. Therefore, the cheat detection is simple. For a period of say, 30 seconds, QuakeForge adds up the times from all the movement packets received from a specific client. If the client says that more then 30 seconds have passed in 30 seconds, a red flag is raised.

Are there any problems with this?

Sadly, the Windows QuakeWorld clients before 2.33 had a bug in keeping track of time. The longer Windows is up, the faster time will seem to pass. While there is not a noticeable speed boost from this until it has been up for more then a day or so, it is detectable even after the system has been up only a few hours.

This and several other factors, including lag and packet loss, can cause the time reported by the client to be over the time the server expects.

Well, what can I do?

QuakeForge's cheat detection is adjustible, so that server admins can decide what settings work best. Here are descriptions of some of the cvars that you can use to configure cheat detection on your server.

sv_timekick: This cvar controls the number of times a player has to be caught "cheating" before they get kicked. sv_timekick shows up in serverinfo if it is changed from the default. If sv_timekick is less than 1, speed cheat detection is disabled. Default is 3.

sv_timekick_fuzz: This cvar affects how strict the protection is. The higher the number, the more "fuzz" is applied, and the less strict the detection code is. Raise this if your players are being kicked for packet loss and lag. The values of this cvar are in tenths of a percent. Default is 10, giving a fuzz factor of about 1 percent.

sv_timekick_interval: This cvar controls how often, in seconds, the time tally is counted. Lowering this value increases the chance of false positives, but helps to minimize the amount of damage a speed-cheating player can cause. Default is 30 seconds.