New anti-malware signatures are automatically downloaded daily, using the Windows Update engine you can also have the software to check for the latest definitions manually. Once the software has scanned your system, you don't need to do anything else, unless it finds malware that it wants to kill or quarantine. The Dynamic Signature Service then determines what action to take against the potential malware. Microsoft says Security Essentials emulates the behavior of programs before they run, and uses the signature created during the process to look for any suspicious behavior or patterns of suspicious behavior, such as starting an unexpected network connection or trying to modify certain protected sections of Windows. Security Essentials uses a new feature called the Dynamic Signature Service, which employs a variety of techniques to check for malware even before that malware's specific signature has been identified. It then launches a quick system scan that took under ten minutes on my system. Once installation is complete, the application downloads the latest anti-malware definitions. Not surprisingly, Microsoft's software won't work with pirated or non-validated versions.

There is one caveat, though: You need to have a validated copy of Windows.

Installation of the 32-bit Vista version on my machine took less than five minutes and was about as simple as an installation can be. Both are light downloads: The 32-bit Vista download weighs in at 4.8 MB, the 64-bit Vista version at 3.8 MB and the XP version (there's only a 32-bit version) comes in at 7.6 MB. Security Essentials comes in versions for XP and Vista (the Vista version will also work with Windows 7).

Microsoft security essentials 32 bit