A false positive, also known as a false detection or false alarm, occurs when an antivirus program detects a known virus string in an uninfected file. The file, while not infected with an actual virus, does contain a string of characters that matches a string from an actual virus. A false positive can also occur when a program performs an action, which appears to the antivirus program to be a virus-like activity. False detections, once confirmed, are usually corrected as soon as possible and an update is issued.

Several competing products are rated higher than Avast, you may want to give one a try. If you do, remember to uninstall Avast before installing another program. Having two at the same time can be a problem. Here is a link that might be useful: PC Mag Anti Virus ratings

I guess this is why it's good not to put all one's eggs in one basket, but use different scans of each type when reasonable (i.e. using online AV scans in addition to using one's preferred full-time AV program). Re: the PC Mag article(s): FWIW, Rubenking praised MBAM -- and I use it myself ! -- but it didn't find the four trojans that the ESET scan did. And my own free Avira AV scan didn't find them either. I'm not sure where trojans fall category-wise: malware or viruses. Or something else. But whatever programs should find them (av or anti-malware), mine didn't. :-( Perhaps I should have also tried AVG just to see if its results would have been better, but I was naturally more concerned with getting rid of whatever was in my computer than with doing AV, anti-malware tests. ;-) So my (albeit limited) experience of having ESET find and remove 4 trojans that MBAM and Avira missed, at least makes me lean in the direction of trusting ESET for future supplementary AV scan purposes. And, of course, I'll try the Kaspersky Virus Removal Tool again if necessary. (Since I ran it after the ESET scan, I have no idea if it would have found and removed the 4 trojans as well. And I hope I never have cause to find out in the future !!)

I had a lot of false positives when I used avast. I goggled them and found one to be very important, it allowed me to communicate with HP for help with my computer. The last straw came when it wouldn't let me play a game that I had always played. I use MS Security Essentials now.