Three stars only because it does not leave my laptop panting for breath. In addition I run Malwarebytes scan every week to double check on these two. This gives me additional protection of sand-boxing, as well as a secondary AV (Comodo AV detection is built in), and there has been no infection in the last 4 years that I am using my Pentium based laptop with Win7. Whether you are logged on to Windows as an administrator. I also have Comodo firewall installed, with Defence+ turned ON. Whether Windows XP, Windows Vista, or Windows 7 is running in a 32-bit or a 64-bit operating environment. I still use MSE as my primary AV, as I find substantial slowing down of my old laptop with either of the other AVs. My personal suggestion is to use AVG or Avast if you need free protection, and have a fast enough PC/laptop with Core i3 or better. It provides real-time protection for your home or small business PCs.

From the developer: Microsoft Security Essentials protects you against viruses, spyware, and other malicious threats. Apparently MS is on a self destructive path, as you can see from the quality of their AV product and the terms they are imposing on potential users of MS office today. You can launch Microsoft Security Essentials on Windows 2000/XP/XP Professional/Vista/7/8/10/11 32 and 64-bit. Microsoft claims that the AV tests are not realistic, as the tests use sample viruses, which have infected only a very small fraction of the total number of PCs running Windows.

It also requires manual updation, as the automatic update never works. MSE today lags behind almost every other AV in virus detection, as mentioned by some of the guys here.

Mse windows 7 64 bit