The iPod virus, was traced back to a computer that was used to test the devices during the manufacturing process. Symantec cited similar instances with other MP3 player manufacturers, such as Creative's Zen Neeon player being shipped with a variant of the Wullik worm last year, and the virus problem with MP3 players given away in a promotion by McDonalds Japan earlier this year.
Symantec said in its October security update "While incidents such as these are not very common, they show that you should always be cautious when connecting unknown media devices such as MP3 players, external disk drives, and USB thumb drives to your computer. Since the viruses present on these devices were already known and antivirus definitions available, you wouldn't be at risk if you connected the device to a computer with up-to-date antivirus software."
The company also explained that in the cases of the iPod and Zen Neeon, you would have to double-click on the files while the device is connected to your computer in order to become infected. However, if you were to connect an infected McDonald's MP3 player to your computer, the virus embedded in the player could infect your computer automatically.
See: www.apple.com/support/windowsvirus/ and www.symantec.com.au