Let me start by saying that I was never a fan of Microsoft’s Live OneCare, their antivirus, firewall, internet security type software. Some time ago, they pulled it from the market; Maybe in part because it didn’t sell very well and because it never really did its job very well, when compared to other products. Microsoft has replaced OneCare with a free new security program called “Security Essentials”.
Security Essentials is designed to be a more light-weight, less invasive antivirus and anti-malware program. It’s made with simplicity in mind; You install it and forget it. Unlike other free security software, it’ll never nag you to upgrade to a “full” version.
I’ve installed Security Essentials on my home PCs and it does deliver on being lightweight and almost completely non-invasive. I don’t think that it’s been out long enough for anyone to really comment on how well it works, though some early reviews are saying that it “holds its own”.
If you need an antivirus software and would like to try Security Essentials, you can download it here: http://www.microsoft.com/Security_essentials/