2006
Support is still on-going
2014
2011
 
Correct Answer: 2014

A brief explanation why…

More than 12 years after it was originally released, Microsoft ended official support including security updates for Windows XP on April 8, 2014, which also marked the conclusion of Office 2003's extended support phase. When support was halted for the platform, it was still running on some 28% of the world's PCs -- nearly quadruple the entire Mac OS user population at the time -- and as of 2016, millions of XP machines remained online.

Although Microsoft would rather you upgrade to a newer version of Windows, you can squeeze another five years of support out of XP with a registry hack that makes it look like you're running Windows Embedded POSReady 2009, a version of XP that's used by systems such as cash registers and will continue receiving support through 2019.