Microsoft Security Essentials is undoubtedly one of the best free anti virus software available today and it runs on Windows without much memory footprint. In case you are running MSE on your PC and it crashed due to any changes you made to registry, then Fix MSE should be able to help you. Fix MSE is a freeware portable utility will reset all the Registry and other settings of Microsoft Security Essentials to default value.
In case you find that you are facing any issues in running Microsoft Security Essentials due to any reasons, simply run this utility. This utility will restore all its registry values & service settings to known good defaults, without re-installing MSE. This utility works fine both on Windows 32 bit and 64 bit PCs.
Supported Operating System:
Make sure that you have Microsoft .Net Framework 2.0 and Microsoft Security Essentials 1.0 installed.