I'm a great believer in using more than one security tool to cover the same area. What one doesn't catch another may. For example, both Panda and Trendmicro have free online scans, which also can remove the malware they detect:
http://www.pandasoftware.com/activescan/ http://housecall.trendmicro.com/housecall/.../start_corp.asp http://fr.trendmicro-europe.com/consumer/p...call_launch.php The last is Trendmicro's new version of its scanner which uses Java, and thus can be used with many browsers and operating systems. I think it may also cover additional types of threats.
Of course, these are on=demand scanners, and aren't resident and running and protecting you all the time, which Norton and for=pay products of Panda and Trendmicro do. I suspect, tho I am not entirely sure, that they detect the same malware as the for=pay versions (i.e., use the same detection engine).
To get the security tool redundancy that I like, you might run a resident program and also carry out periodic scans. For example, Norton might be the resident, and Panda and Trendmicro might be the scans.
However, while all this would provide pretty good redundant protection against viruses, it would provide much less protection against Trojans and adware/spyware. I think that these days protecting only against viruses is a mistake. For Trojans there is a=squared and Ewido. For adware/spyware there is AdAware and SpyBot Search and Destroy. Spybot is free; the others are free as scanners, for=pay when resident.