Apple Mobile OS version 3.1.3 is out today. Install it... it patches
three arbitrary code execution vulnerabilities that can be exploited by
(respectively) viewing a TIFF image, accessing an FTP server, or playing
an mp4 audio file. Yuck! Oh yeah, it also plugs a hole where a person
who gets a hold of your device can bypass the lock screen by sending a
well-crafted command to your USB port.
-Greg Mackinnon (sent from my desktop, because the iPod is being patched)