Microsoft is to end support for Windows XP on 8 April, 2014, leaving 31 per cent of desktops that still run it vulnerable to hackers.
According to a report by Net Market Share, Windows XP is second only to Windows 7 (46 per cent) in terms of desktop user share. By ending support and no longer issuing security fixes, Microsoft will leave millions of users susceptible to attacks from hackers.
On Microsoft's Support Ends website, the company explain that Microsoft Business and Developer products receive a minimum of 10 years of support, but after that there is no guarantee.
"If your organization has not started the migration to a modern desktop, you are late," the company says. "Based on historical customer deployment data, the average enterprise deployment can take 18 to 32 months from business case through full deployment."
It is advised by Microsoft that those customers who have not started the migration should take action.
"After April 8, 2014, there will be no new security updates, non-security hotfixes, free or paid assisted support options or online technical content updates," the company warns.
The potential risks include control failure by an internal or external audit body, suspension of certificates and public notification of the organisation's ability to maintain its systems and customer information.
A recent report from Gartner research also suggests "many independent software vendors (ISVs) are unlikely to support new versions of applications on Windows XP".
Three days ago, Microsoft issued a warning that there was a security flaw in Windows XP, releasing an emergency patch to close the loophole.
"Microsoft is investigating new reports of a vulnerability in a kernel component of Windows XP and Windows Server 2003," the statement read. "We are aware of limited, targeted attacks that attempt to exploit this vulnerability."