Microsoft has announced that they will end support for Windows Server 2003 in July of 2015.
All software products have a lifecycle. End of support refers to the date when Microsoft will no longer provide automatic fixes, updates, or online technical assistance. (link is external) As of July 2014, there were 12 million physical servers worldwide still running Windows Server 2003.
Computers running the Windows Server 2003 operating system will continue to work after support ends. However, using unsupported software may increase the risks of viruses and other security threats. Negative consequences could include loss of confidentiality, integrity, and or availability of data, system resources and business assets.
Users have the option to upgrade to a currently supported operating system or other cloud-based services. There are software vendors and service providers in the marketplace who offer assistance in migrating from Windows Server 2003 to a currently supported operating system or SaaS (software as a service) / IaaS (infrastructure as a service) products and services.
Read the US-CERT alert at https://www.us-cert.gov/ncas/alerts/TA14-310A