Microsoft Security Essentials is no longer available for Windows XP .

Is my PC at risk now that support has ended for Windows XP?

PCs running Windows XP after April 8, 2014 should not be considered to be truly protected.

Support ended for Windows XP on April 8, 2014. Microsoft will no longer provide security updates for Windows XP to help protect your PC against malware. Microsoft has also stopped providing Microsoft Security Essentials for download on Windows XP. If you already have Microsoft Security Essentials installed, you will continue to receive Microsoft Security Essentials updates for a limited time * to help identify malware on your PC while you complete your transition to a fully supported operating system. The Malicious Software Removal Tool will continue to be provided for Windows XP for a limited time * through Windows Update and the Download Center.

Please note that since the above real-time protection products have limited effectiveness on PCs that do not have the latest security updates, your PC will still be at risk for infection.

We strongly recommend that you complete your migration to a supported operating system as soon as possible so that you can receive regular security updates to help protect your computer from malicious attacks.

* The Malicious Software Removal Tool and updates to Microsoft Security Essentials will continue to be provided for Windows XP through July 14, 2015.    

courtesy:http://windows.microsoft.com