101 Fantastic Freebies
Great for checking potentially dangerous downloads and e-mail attachments, this uploader gives you a right-click option to send any file under 10MB to VirusTotal's exceptional site, where you'll receive antivirus scan results from 32 different program engines.
Avira AntiVir PersonalEdition
Avira typically does a great job of detecting malware on a PC; the paid version of the program posted a 99.6 percent catch rate in the latest tests from AV-Test.org. The free version employs the same engine, but you'll have to tolerate the occasional pop-up urging you to upgrade to the paid application.
Spyware Doctor Starter Edition
This edition of the popular PC Tools antispyware application is part of the Google Pack. The free version can run full spyware scans but doesn't have many of the real-time protection features of the paid version.
Comodo Firewall Pro
Comodo's extensive firewall can block unauthorized attempts to send information from your PC to the Internet, which surpasses the protection that the built-in XP firewall offers. But as with any advanced firewall, be sure you know what you're doing before monkeying with the more in-depth security settings.
Create an encrypted virtual drive with its own drive letter that automatically protects any file you add to it with your choice of encryption. If you try this program, be sure to go through the helpful first-time-use tutorial.
Secunia Personal Software Inspector
Secunia's useful program makes keeping your software applications up-to-date much easier. It even covers apps that you might rarely use but that can leave Internet Explorer (and your PC) wide open because of an unsafe ActiveX control. PSI provides details on the security holes in old software and tells you where to obtain updates.
Spamfighter harnesses the collective intelligence of 4.5 million e-mailers around the world to block spam with a toolbar in Outlook, Outlook Express, and Windows Mail. The free Standard version shows a text ad in the toolbar and adds a footer to your e-mail messages. (A Pro version is ad-free and costs $29 after a 30-day trial.)
BitDefender Online Scanner
If you suspect that your regular antivirus app missed a malware infection, head to BitDefender's online scanner (requires Internet Explorer) for a second opinion. The Web app scans your system's memory and all files, detecting and removing infections.
ThreatFire supplements (but doesn't replace) your regular antivirus program. It adds behavioral-analysis protection that attempts to identify Trojan horses and other malware based on how they act on your PC.
McAfee Rootkit Detective
The information you receive from Rootkit Detective's pursuit of malware-hiding rootkits might be too technical to use yourself. The handy Submit button, however, will produce free advice on dealing with the suspicious files it finds.