Microsoft Security Essentials is a free* product you can download to help defend computers running Windows Vista and Windows 7 against viruses, spyware, and other malicious software.
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.
Easy to get, easy to use—Microsoft Security Essentials is available at no cost, so there's no registration process that requires billing or personal information collection. It installs after a quick download and then stays automatically up to date with the latest spyware protection technology and signature updates.
Quiet protection—Microsoft Security Essentials doesn't get in your way. It runs quietly in the background and schedules a scan when your computer is most likely idle. You only see alerts when you need to take action.
Microsoft Security Essentials has a clean, simple home page that shows the security state of your computer.
A green icon means that the security status of your computer is good. Microsoft Security Essentials is up to date and is running in the background to help protect your computer against malware and other malicious threats. When your computer has an issue that requires your attention, the look of the Microsoft Security Essentials home page changes based on the issue. The status pane turns either yellow or red depending on the situation, and an action button appears in a prominent location on the page with the suggested action.
A yellow icon means that status is fair or potentially unprotected and that you should take some action, such as turning on real-time protection, running a system scan, or addressing a medium-severity or low-severity threat.
A red icon means that your computer is at risk and that you must address a severe threat to protect it. Click the button to take the recommended action and Microsoft Security Essentials will clean the detected file and then do a quick scan for additional malicious software.