"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," they explained in a blog post.
"For enterprise customers, this applies to System Center Endpoint Protection, Forefront Client Security, Forefront Endpoint Protection and Windows Intune running on Windows XP. For consumers, this applies to Microsoft Security Essentials."
The decision was likely influenced by the fact that some 30 percent of users have yet to switch to a newer version of Windows, and it seems they are not in a hurry, despite Microsoft having been very vocal about the scheduled end of support date for one of their most popular OS versions.
"Our research shows that the effectiveness of antimalware solutions on out-of-support operating systems is limited," they warn, though. "Running a well-protected solution starts with using modern software and hardware designed to help protect against today’s threat landscape."
Another important thing to consider is that security researchers predict that the number of active campaigns using Windows XP exploits will escalate.
If you insist on using the old OS you must be aware that even if Microsoft's security solutions still receive new signatures, it doesn't mean you are safe.
While you consider a move to one of the newer versions, here is a list of alternative AV solutions you can use in the meantime.