Avast! Free Antivirus is my new top pick for the best free antivirus software in light of recent developments. Avast has steadily been improving its detection rates over the past few years and now ranks with the some of the best. Avast has the most features of all the free antivirus with full real-time capabilities including web, e-mail, IM, P2P and network shields, boot-time scanning, and a behavioural blocker. Version 6 brought even more features including an internet site ratings plugin, script malware protection and a limited (non-configurable) sandboxing feature. It's arguable whether their ratings plugin offers comparable levels to WOT, but the script malware protection can prevent certain browser exploits, a feature not available in any of the other free AV's. Although the sandbox is a very useful semi-automated security feature, the default settings involves a pop up to ask whether a software should be sandboxed for not - for the typical average user this can be slightly confusing though it can set to sandbox the software automatically. Avast is also relatively light on resources. Note that Avast requires a free registration to function after 30 days.If you think your PC has been infected by something, but your regular antivirus tool hasn't raised an alert, then it could be time to grab a copy of Malwarebytes Anti-Malware Free.
The program is an excellent real-time scanner which can quickly find and remove all kinds of threats.I use both together on my computer have been for over a year no issues.