Prior to support ending for Windows XP, Microsoft advised that the Malicious Software Removal Tool (MSRT) would continue to be updated and deployed via Windows Update through July 14, 2015. However, MRST is still listed for Windows XP under system requirements for Supported Operating System
and on the MSRT Summary page
...most likely due to the third quote below in regards to retaining a weapon.MPC Threat Research & Response Blog: Microsoft Extends Antimalware Support for Windows XP
Microsoft will furnish malware assassin to XP users until mid-2015
Microsoft has announced the Windows XP end of support date of April 8, 2014. After this date, Windows XP will no longer be a supported operating system. To help organizations complete their migrations, Microsoft will continue to provide updates to our antimalware signatures and engine for Windows XP users through July 14, 2015. This does not affect the end-of-support date of Windows XP, or the supportability of Windows XP for other Microsoft products, which deliver and apply those signatures.
Microsoft retains weapon to silently scrub XP
"Microsoft's Malicious Software Removal Tool is aligned with the company's anti-malware engines and signatures, and as such the removal tool will continue to be provided for Windows XP through July 14, 2015...
Microsoft will be able to silently reach into Windows XP PCs for more than a year after it stops patching the aged OS to clean malware-infected machines, sources close to the company confirmed Friday. The Malicious Software Removal Tool (MSRT) will continue to be updated and deployed via Windows Update through July 14, 2015, 15 months after the Redmond, Wash. company serves its final public security patches for XP on April 8 of this year. By extending the life of the MSRT -- and more importantly, automatically running it each month -- Microsoft will be able to clean some PCs if massive malware outbreaks hit Windows XP after it's retired from support....With MSRT, Microsoft will have a weapon at the ready in case widespread malware infections strike XP machines after April 8, something the company has said is likely.