While viruses for Symbian and Windows Mobile currently seem more like proof-of-concept studies, the Windows Mobile platform offers malware writers who already know Windows a very similar environment. Some may call it a hype, but that's what people said about spyware 5 years ago as well, and our opinion is that it's better to protect yourself before something happens than to do it afterwards. Spybot-S&D for Windows Mobile uses a lightweight version of the detection engine of Spybot-S&D for Windows to detect threats for Windows Mobile and Symbian both, the later because Bluetooth worms could spread over OS borders, and while they would not perform on an incompatible OS, they would still waste precious space on the device.
Windows Mobile 5.x
Windows Mobile 2003 Phone Edition
Windows Mobile 2003
Pocket PC 2002
Windows Mobile 2003 SE
Pocket PC 2002, Windows Mobile 2003/2003 Phone Edition/2003 SE/5.x