I run Windows 7. A few weeks ago I uninstalled Microsoft Security Essentials (MSE) because it was taking up so much of my CPU, and downloaded Avast (the free version). After a couple of weeks I discovered that Avast had been completely uninstalled and MSE was back as my antivirus programme. I uninstalled MSE again using Revo Uninstall, and re-downloaded Avast. Today I found that the same thing had happened - Avast was no longer on my computer and MSE was back again. Once again I have uninstalled MSE and re-downloaded Avast. Can anyone advise me how to prevent this happening, and also how it is happening? Could it be the Windows Updates that are doing this?