I know we as MacUsers don't have a lot to worry about (yet), but it's reassuring to have a programme like this to run occasionally. I don't keep it active all the time, just a reassuring scan every couple of weeks. Of all the anti-viral programmes, this seems to be the best: easy to use, doesn't hog resources, is updated regularly, and best of all, it's free. The web site provides support and is informative. What's the catch?