Government systems running Windows XP will reportedly become more vulnerable to attacks after Microsoft ends supporting the OS on April 8th. The deadline will also affect banks as more than 95 percent of the world's ATMs run on Windows XP.

Microsoft Windows XP supports over four million government computers in the US alone and the lack of security updates post the deadline will make them more prone to exploits and malware. Microsoft is offering paid support extension for governments and businesses, but this service could prove more costly in the long run than upgrading to Windows 7 or 8.

RBS is upgrading its machines to Windows 7 which will take about three years to complete. JPMorgan has also started converting its machines to Windows 7 which will be completed by the end of this year. Lloyds has extended its support contract with Microsoft to 2016 while it updates 7,000 units. HSBC and Santander have agreements in place with Microsoft already, while Barclays is still negotiating a deal with Microsoft.

"There are certainly large enterprise customers who haven't finished their migrations yet and are purchasing custom support," a spokesman for Microsoft said, declining to name those customers or to quantify the extra revenue it is earning. "The cost will depend on both the specific needs of the customer and what support they already have in place, so it's different for every customer."