i have seen a few discussions here about virus, trojan horse stuff here. here are tips for windows users:
1. keeping up with windows update. well, dont get yourself into trouble if you are using pirated version.
2. keeping virus definition for your anti-virus program updated.
3. be cautious about any executable files.
4. backing up critical stuff.
there are a couple of freebies for anti-virus and anti-spyware. downloading a free version of anti-spyware such as ad-aware to run though your hard drive, you would be surprised when you see those spywares. alright, it is time to knock yourself out.