There's a new Cold War in town, and the Internet is ground zero. Once upon a PC, you were unlikely to encounter a virus or Trojan horse online. Hostile code infiltrated your system passively: through trading software with associates, from shrink-wrapped packages in stores, or even stamped onto your hard drive on a new system (as was the case with Michelangelo).

Times have changed, and so have viral attack vectors. There's a much larger audience for online services, and consequently, a new slew of malicious software writers looking to make their mark. Viruses have achieved stealth, and worms have been taught how to propagate themselves through popular e-mail packages. And antivirus programs have had to learn new tactics to defend your PC.

The software packages reviewed here contain several common elements. Scanners perform guard duty and reconnaissance, monitoring your system's activities and browsing through files looking for known code that could contain a virus or Trojan program. Signature or definition files provide the scanners with the blueprints for new viruses and need to be updated regularly to effectively defend the perimeter. A cleanser will actually eradicate the virus, or if need be, erase or quarantine the contaminated files.

We tested each product with at least one quarantined virus we caught "in the wild," and with a test file from the European Institute for Computer Anti-Virus Research. Each program effectively tracked and cracked the code we bombarded it with. Therefore, the following reviews will focus on those elements that will help you choose the one that best suits your needs.

Many effective antivirus solutions are available. In fact, there has been so much competition (and occasional litigation) between the leading contenders that it can be difficult to determine which feature set is best for your needs. To help answer that question, we looked at Computer Associates' InoculateIT Personal Edition 4.5, Network Associates' McAfee VirusScan 4.03, Symantec Corp.'s Norton AntiVirus 2000 in beta, and Trend Micro's PC-cillin 6.