Microsoft Security Essentials provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software. Microsoft Security Essentials is a free* download from Microsoft that is simple to install, easy to use, and always kept up to date so you can be assured your PC is protected by the latest technology. It’s easy to tell if your PC is secure — when you’re green, you’re good. It’s that simple. Microsoft Security Essentials runs quietly and efficiently in the background so that you are free to use your Windows-based PC the way you want—without interruptions or long computer wait times. http://www.microsoft.com/security_essentials/ so far so good. i can't even tell it's running on my computer, and that's while it's scanning. this isn't really a deal because it is guaranteed to be free. it should be noted that this only works for windows computers.
i don't believe there was ever a paid version for MSE. might you be referring to live onecare? onecare was pretty bad.
The big question is whether it will be in conflict with other anti-virus software being in used, such as Norton, McAfee, etc.? I assume this is a realtime application that protect you running in background. Real time protection applications tend to have more conflict than the on demand ones.
