See also Trojan horse.

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.

Detecting and Removing RATs
If a computer virus or email worm has ever infected your company, the company is a prime candidate for a RAT. Typical antivirus scanners are less likely to detect RATs than worms or viruses because of binders and intruder encryption routines.

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