Spybot - Search & Destroy for Pocket PC 0.3 
2.63 MB, freeware, rate:  
Spybot - Search & Destroy for Pocket PC detects and removes spyware, a relatively new kind of threat not yet covered by common anti-virus applications
more info screenshot

Trend Micro Mobile Security 2.0.0.2146 
2.8 MB, shareware, rate:  
Trend Micro Mobile Security features an easy-to-use mobile handset interface that simplifies protection from viruses and SMS text message spam
more info screenshot

F-Secure Mobile Anti-Virus 2.1 Build 11510 
1.3 MB, shareware, rate:  
F-Secure Anti-Virus protects your Pocket PC against viruses, spyware, worms, and Trojans. Protection is needed on every smartphone to secure the continuously increasing mobile communication
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avast! 4.1.16 PDA 
98 KB, shareware, rate:  
avast! PDA Edition is designed to protect pocket devices (PDAs) from viruses. The importance of PDAs is growing every day and it is quite likely that these devices will soon become a target for new virus attacks
more info screenshot