A recently posted BugTraq listing (thanks 3DGPU) outlines a vulnerability in Epic's Unreal engine that's susceptible to DoS, DDoS and bounce attacks with spoofed UDP packets. The report outlines the problem, which affects dozens of games from Unreal through UT2003, and describes how the author of the report held off on publicizing this for almost three months to give time for Epic to devise a fix. I contacted Epic's Mark Rein to ask about this and he was very frank about how this had indeed been brought to their attention, but had unfortunately fallen through the cracks. He sent along a list of changes for the next planned UT2003 patch which will now address these vulnerabilities, and says it's likely that a small patch will be issued to address these in the original version of Unreal Tournament as well. As for other games using the Unreal engine, he says that fixes like this are always made available to licensees, who will then be able to issue patches of their own should they so choose. Here is Mark's no-holds-barred assessment of why this went unaddressed after being brought to their attention:

I won't sugar coat this. We f***ed up on this. Yes this is real and yes this was brought to our attention and yes we should have fixed it by now. We are working on fixing this now and we will have this fixed in an upcoming patch before too long.