Microsoft has announced that they will continue to supply anti-malware signatures for their products on Windows XP until April 15, 2015.
There has been much speculation in about whether they would continue this support. In October Microsoft told ZDNet that they "...will not guarantee updates of our antimalware signature and engine after the XP end of support date of April 8, 2014." Since then some have claimed that the company will end antivirus signatures this April, but Microsoft never actually said this.
[UPDATE: While Microsoft will provide updates for Security Essentials for another year, after this April you will no longer be able to download and install the program.]
Even if Microsoft Security Essentials will continue to be updated after April, moving to a supported operating system which receives security updates is advisable according to Microsoft and experts. Users who continue to run XP also have the option of many third party anti-malware products, virtually all of which will continue to receive updates on XP for at least one year.
As Microsoft's announcement today says, there is much more to keeping a system secure than an updated anti-malware product.