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In Windows 8.1 and Windows RT 8.1, Windows Defender provides the same level of protection against malware as Microsoft Security Essentials. You can't use Microsoft Security Essentials with Windows 8 and Windows RT, but you don't need to—Windows Defender is already included and ready to go.
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Get answers to your questions in the Windows Defender forum.
Get help from a support professional.
Getting started with Microsoft Security Essentials
Alert levels in Microsoft Security Essentials
Is my PC infected with viruses or spyware?
How do I uninstall antivirus or antispyware programs?
How do I know that Microsoft Security Essentials is running on my PC?
What should I do if Microsoft Security Essentials detects malicious software on my PC?
Will my scan catch even the most recent viruses?
Frequently asked questions about malicious software
I can't install Microsoft Security Essentials
I can't start the Microsoft Security Essentials service
My PC runs slowly after installing Microsoft Security Essentials
Errors during virus and spyware definition updates or product upgrades
Troubleshooting update issues for Microsoft Security Essentials
Get answers to your question in the Virus and Malware forum.
Can’t find answers to your questions? Submit a support case.
If you believe that files on your PC are viruses, spyware, trojans, worms or other malicious software that should be detected by Microsoft Security Essentials, but haven't been, you can send these files to Microsoft.
As of April 8, 2014, support and updates for Windows XP are no longer available.
Find out how to stay protected.