This is a replacement of the not-too-popular Windows Live Care anti-virus software (did anybody even use that?). It looks as though MS plans to have an anti-virus application that they may keep free, along the lines of Windows Defender in the spyware protection arena.

This would then make Security Essentials a competitor to the lower-end free AV solutions such as the free editions of AVG and Avast.

The Ars Technica story is here

Lifehacker has a great breakdown here

Go directly to the Microsoft Security Essentials beta site here