As most Win 8.1 users know, the older versions of Avast are not compatible with Win 8.1 This new version 2014.9.0.2007 is compatible. I just installed the FREE edition, and it works. It has email scanning option, I have it disabled. http://www.avast.com/en-ca/index I decided to install Avast, in light of the disturbing report/review of Windows Defender, aka MSE, being at the bottom of the review list and that even MS recommends users to use 3rd party program. excerpt: In an interview with Dennis Protection Labs, Holly Stewart, the senior program manager of the Microsoft Malware Protection Center, said that Microsoft Security Essentials was just a “baseline” that’s designed to “always be on the bottom” of antivirus tests. She said Microsoft sees MSE as a first layer of protection and advises Windows users to use a third-party antivirus instead. Source to read the entire article.