After the April 8, 2014 some Microsoft products are no longer supported; Windows XP, Server 2003, Exchange 2003, Office 2003 … It is estimated that 30% of desktop operating systems are Windows XP.
Why you should be concerned.
Here’s a possible scenario. Let’s say that Windows 7 shares some code with Windows XP and an exploit is discovered that effects both. The security patch will be released for Windows 7 but not the discontinued Windows XP. Attackers can reverse engineer the patch to discover the effected code and then test the exploit against Windows XP.
This is not as unlikely as it might sound. Have a read of : Microsoft Security Blog
Between July 2012 and July 2013 Windows XP was an affected product in 45 Microsoft security bulletins, of which 30 also affected Windows 7 and Windows 8
It’s not advisable to have these end of life products on your network after April 8. If attackers get into a vulnerable machine it makes it easier to exploit other machines on your network.
The worst possible scenario is having Windows XP machines running Office 2003 and using Server 2003 or Exchange 2003. That’s just asking for trouble.
Hopefully most folks are either upgrading or shutting down these machines after April 8. If you have to run any of these, I suggest that you isolate that machine.