This is a Beta product so it may not be 100% reliable, but it looks promising. It only works (of course) on the Chrome browser.
Noted in passing in "Superfish injects ads in 4% of Google page views | Computerworld"
All it does is look at Chrome browser settings, check extensions and plugins added to Chrome against its own blacklist/whitelist, stuff like that. No scan engine involved I suspect. It took about 5 seconds.