I tried it some time ago, I think at the time they were offering a free version. While it claims to be compatible with avast! antivirus click here my copy of avast didn't like it at all, reporting assorted nasties in it. As I trust avast and not ewido I ditched it. Now this may well have been early development bugs that have been removed, but as they now want $29.95 for it and a² click here and prevx home click here are free I've seen no point in looking twice.
You initally get a trial version with real time monitoring which reverts to a free version after the trial period is over. The free version doesn't have real time monitoring. It updates two or three times a day if you set it for automatic updates.
From their site : "After the installation, a free 14-day test version containing all the extensions of the plus-version will be activated. At the end of the test phase, the extensions of the plus version are deactivated and the freeware version can be used unlimited times."
It's very handy for scanning programmes that you download, (you can do it from the right click menu). Worth having in my opinion and it's free.
I had it running happily on XP pro and it was as bertiecharlie says. It didn’t catch anything but I don’t think that was necessarily because of any inability on its part. The only reason I don’t have it back on now is I’m trying a few other bits out.