Microsoft ends updates for Security Essentials on XP
Microsoft ended official support for Windows XP in April last year, which means no security patches for the OS (except for a few select large customers such as the U.S. Navy), but they continued to issue updated signatures for the Security Essentials anti-malware software that was already running on XP for a then-unspecified period of time.
All good things must come to an end, though, and this one just did. There will now be no more updates for the tool on XP systems, which means an ancient (in compputer years) and increasingly non-secure operating system just got even more so. If you have XP systems still running on your network (including those used by telecommuters or weekend at-home workers who connect to your corporate network), it's past time to do something about it.