Windows XP support ended on April 08 2014 and the following statement is taken from Microsoft’s website.
What happens if I continue to use Windows XP?
If you continue to use Windows XP now that support has ended, your computer will still work but it might become more vulnerable to security risks and viruses. […] Also, as more software and hardware manufacturers continue to optimize for more recent versions of Windows, you can expect to encounter more apps and devices that do not work with Windows XP.
Well, this week those Windows XP users who are running iTunes on their out of date machines certainly found out the hard way.
When logging on to iTunes, Windows XP users get the following message ‘An unknown error occurred (error 0x80090326).’ This means they can’t buy content, watch purchased movies and TV shows, play DRM-protected content, backup, update or sync.
Many users have wasted time and effort troubleshooting their machines but it is thought that Apple changed something to do with the secure connection iTunes uses to connect to the iTunes store and did not test the changes on Windows XP.
It has been speculated that an update adding support for two new ciphers (both of which work on the RC4 algorithm and are not supported by Windows XP) is connected to the problem and only time will tell if Apple will makes changes to rectify the problem.