“I could not get my Windows Defender to work after installing Microsoft Security Essentials. Why?”
Windows 7 and Windows Vista both come with antispyware software called Windows Defender. If you want to protect your computer from more than spyware, you can install Microsoft Security Essentials for free.
Because you don’t need both programs, when you install Microsoft Security Essentials it will automatically disable (but not uninstall) Windows Defender. For more information, see Do I need both Microsoft Security Essentials and another antivirus software program?
Need security for your business?
Microsoft Security Essentials is available for small businesses with up to 10 PCs. If your business has more than 10 PCs, you can protect your computers with Microsoft Forefront Endpoint Protection.