For the last few days, some jailbroken iPhone users have found their home screen background a little different than they remembered. A hacker, going by the name "ikee," created a worm that changes the home screen background on jailbroken iPhones whose owners failed to change the default password after installing SSH.
Simply jailbreaking your iPhone will not make you vulnerable to this sort of hack. The iPhone OS, in general, is also immune to this hack. On jailbroken iPhones, SSH is installable with a package from Cydia that allows you to connect to your phone and make changes to the filesystem.
(Source: TUAW News)