As posted on the mailing lists a few days ago:
Hi everyone. In response to a few UT3 hacks released, we have an updated EXE for dedicated server operators that shuts these exploits down.
If you're running a Windows dedicated server, please download and apply this exe: http://www.epicgames.com/download/ut3.exe.
This exe requires the v1.3 patch. This file is for dedicated servers only and doesn't introduce any new features over v1.3 other than the hack fixes.
Please PM me if you have any questions. Thanks!