Also see The Difference Between a Virus, Worm and Trojan Horse in the Did You Know? section of Webopedia.

Symantec Security Response
Our security research centers around the world provide unparalleled analysis of and protection from malware, security risks, vulnerabilities, and spam.

Symantec Technology Web Site
The official Web site for Symantec Corp.

Webopedia Quick Reference: Common Windows PC Issues
Tips to Diagnose and fix a slow running computer.

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