Follow along with the video below to see how to install our site as a web app on your home screen.
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My recommendation, Microsoft Security Essentials for Windows, it's free, has similar scores to all other major antivirus in virus detection tests and it's not a resource hog: http://windows.microsoft.com/en-US/windows/products/security-essentials
For the Mac, Sophos: http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx