If you are running a version of Windows that is no longer supported you need to be aware that once an operating system is no longer supported no further Microsoft Updates will be issued for that operating system. Such operating systems then become prime targets for malware infestations and will become infected.
http://windows.microsoft.com/en-us/wind ... pport-mean
Support for Windows Vista Service Pack 1 (SP1) ends on July 12, 2011. To continue support, make sure you've installed Windows Vista Service Pack 2 (SP2).
Support for Windows Vista without any service packs ended on April 13, 2010. To continue support, make sure you've installed Windows Vista SP2.
Support for Windows XP with Service Pack 2 (SP2) ended on July 13, 2010.
To continue support, make sure you've installed Windows XP Service Pack 3 (SP3).
IMPORTANT: The above mentioned Service Packs should only be installed on a malware free computer.
Support for Windows XP SP1 ended on October 10, 2006.
Support for ALL versions of Windows XP ended on April 8, 2014.