If you are a fan of Internet Explorer then you may have noticed the Smart screen Filter which is practically a dynamic list of known “illegal, viral, fraudulent, or malicious” URLs that Microsoft manually or algorithmally identifies. It uses this list to compare the link or executes a user visits or downloads, warning if there’s a match.This function is also present in the latest version of Messenger that is the Live Messenger 2011. Now Microsoft is planning to include this "SmartScreen" feature in Windows 8.
According to an article posted HERE ,In Windows 8, SmartScreen appears to serve two purposes – to reactively check the file system and proactively prevent any downloaded applications from running that are unknown to the filter.This addition mechanism adds to a growing list of security-centric features and tools including but not limited to digital signing, User Account Control, Windows Defender and Security Essentials that Microsoft is building into Windows or making available for free.
One thing I liked about Microsoft that there is a option to turn it off as you can see in the above screenshot .Because who knows, it may become annoying and may be need to turn it off. But I can definitely say that Microsoft is trying very hard to make it’s next OS more secure than ever before.