Look out if you are running a device with iOS 3.1.2 or higher; it seems that you can let a hacker into your device simply by loading a PDF file. This security bug, which is also used for programs like JailbreakMe that we reported on yesterday, can give one click access to your device and bypass Apple's security.
Apparently all it takes to let someone in is to load a PDF in Safari that contains a font that hides the rogue program, causing "stack overflow" that allows the program access to the device. The rogue programs can install, delete, or monitor programs on the device without the user knowing. There are a few workarounds besides the obvious "only open files from trusted sources," such as PDF loading warner apps from Cydia to remind you of the possibility of intrusion.