Dynamic Signature Service
With the release of Microsoft Security Essentials, Microsoft is introducing Dynamic Signature Service, a new approach to providing the most up-to-date protection for the PC without having to wait for the next signature download. In addition to validating suspicious files against the set of signatures that are downloaded daily, Microsoft Security Essentials contains additional technology to monitor for new and emerging malware and check for signature updates in near-real time.

A new class of heuristic signatures leverages Microsoft’s dynamic translation technology to emulate the behavior of a program before it runs. Microsoft Security Essentials uses these signatures to look for signs of suspicious behavior, characteristics that are similar to known malware and other abnormal operations, and then queries the Dynamic Signature Service to see if the program should be submitted for analysis or terminated.

After a process starts, Microsoft Security Essentials also monitors the file, registry, network and kernel mode actions taken by unknown programs to look for suspicious behavior. Actions such as initiating unexpected network connections, attempting to modify privileged parts of the system, or downloading known malicious content all trigger requests for updates from the Dynamic Signature Service.