It's a handheld computer. I haven't heard of any exploits but what do I know?
I used Antivirus FREE by droidSecurity Inc for a few months. I then elected to buy their AntiVirus PRO version for $9.99. Quote from their website, "...Pro enables remote management of lost/stolen phones along with tracking of illicit phone usage in the case of theft."
You can get them on the Android Market. Search for "Antivirus Free" or "Antivirus Pro." The free version worked fine. With more than 250,000 downloads and 24,175+ ratings it holds a 4.24 avg.
Norton Security is also free. As I'd never use a Norton Product on my laptop, I wouldn't use one on my Handheld Computer.
Good Luck!