Luigi Auriemma

a format string exploitable from outside the server of games like Doom 3, Quake 4 and Prey:

http://aluigi.org/adv/d3engfspb-adv.txt

There is also a video available here:

http://aluigi.org/video.htm
http://www.youtube.com/watch?v=SvzGqFlNZOo

nice discovery. ..so basically its something like buffer overflow ?
i dont have any of those games anymore...

A format string allows code execution so, although it's different than buffer-overflow (aaaaaaa...aaaa), it has the same final effect.
In C there are the functions of the *printf family in which you can specify a string (called format argument or string) that is used to show numbers in hex format, or in decimal format, or parts of text strings and so on: %s %n %f %c %d %u %o and so on.
When this format argument is missed the user supplied string will be used as format allowing the attacker to take control of the stack.