Microsoft have annouced that on 8th April, 2014 they will end their support for Windows XP operating system.

It means there will be no new security updates or non-security hotfixes. Running Windows XP SP3 in your environment after their end of support date may expose your company to potential risks, such as Security & Compliance Risks and Lack of Independent Software Vendor (ISV) & Hardware Manufacturers support.

For the complete details see the Full Microsoft Announcement

Note: This does NOT include Windows XP Embedded, where the phase out date is extended (currently January 2017)  http://www.microsoft.com/windowsembedded/en-gb/product-lifecycles.aspx