MHX First Defense
A previous version of the program looked only for a small number of known malicious programs (or processes) actively running on your PC. While the latest, 3.3.1 version adds scans for known malicious files on your hard drive or other selected locations that don't have to be active at the time of the scan, the signature database it uses to recognize threats is still very small compared to better-known antivirus programs.
When we tested it, MHX reported having 11,842 antivirus and antispyware definitions in its signature database. By contrast, AVG Anti-Virus Free had 1,471,137 definitions at the same point in time.
While running, MHX can eat up a large amount of system resources. Even with its active protection turned off, and with no scans running, it occasionally used as much as 60 percent of the cpu.
Toss in an unavoidable nag screen at every program close that stays up for 15 seconds and then launches the developer's Web page in your browser, and there's not much reason to choose MHX over other free products, let alone pay $3 (in Canadian dollars) for a Pro version that clears that nag screen and adds a registry scanner.