For those of you out there using one of the real browsers (among others, I am pointing at Firefox), you might find that version 3 of Firefox, while being a brilliant browser for the rest, built-in virusscan on completed downloads is a bit annoying. In my case, it always freezes for about two seconds while initiating the scan. Plus, having a good virusscanner already active, I don’t really see the point.
You can disable this feature by typing about:config in the address bar, and then filtering on browser.download.manager.scanWhenDone. Double click this line to set the value to false.