See The Difference Between a Virus, Worm and Trojan Horse in the Did You Know? section of Webopedia.
Also see Preventative Maintenance Tips for Your PC in the Did You Know? section of Webopedia.

eSecurity Planet 
A resource for daily information on e-security targeted to IT managers. The site provides users with information from a variety of sources, including experts at security product and services firms, and the consultants who follow the security industry.

Webopedia's "Did You Know?" Article
The Difference Between a Virus, Worm and Trojan Horse.

Webopedia's Quick Reference Section
Use this Webopedia reference section for information on common Internet and computer facts and occurrences.