Note: In Windows 8, Windows Defender replaces Microsoft Security Essentials. Windows Defender runs in the background and notifies you when you need to take specific action. However, you can use it anytime to scan for malware if your computer isn’t working properly or you clicked a suspicious link online or in an email message.
Comprehensive protection—Microsoft Security Essentials helps defend your computer against viruses, worms, Trojans, and other malicious software and provides you with free spyware protection.
Quiet protection—Microsoft Security Essentials runs quietly in the background and schedules a scan when your computer is most likely idle.