CHQ has warned people not to do internet banking or use emails from computers with Windows 7 from Tuesday, when Microsoft will end support for the software.
The National Cyber Security Centre (NCSC), the public-facing arm of the cyber spy agency, said that devices still using the operating system after next week will become increasingly vulnerable to cyber attacks as the tech giant stops patching weaknesses in its product.
Microsoft announced last year that it would be ceasing technical support for Windows 7 and urged users to upgrade to its Windows 10 system, which costs £120.
It is estimated that there are still more than 440 million people using Windows 7 worldwide, which was first released in 2009.
A spokesperson for the NCSC said: “The NCSC would encourage people to upgrade devices currently running Windows 7, allowing them to continue receiving software updates which help protect their devices.
“We would urge those using the software after the deadline to replace unsupported devices as soon as possible, to move sensitive data to a supported device and not to use them for tasks like accessing bank and other sensitive accounts.
“They should also consider accessing email from a different device.”
The national security agency warned that after Microsoft stopped supporting Windows XP in 2014 that hackers soon started exploiting weaknesses in the system.
The NCSC spokesman added: “As a result, it’s crucial to move away from them as quickly as possible.”
The Windows 7 operating system has previously been caught up in security lapses. In 2017, most of the NHS computers infected by the WannaCry ransomware attack, which caused almost 19,500 hospital appointments – including cancer referrals – to be cancelled, were found to be using the operating system.
However, report into the hacking, which affected 81 trusts in England and Wales, found that many of the systems had not been updated by NHS groups leaving them more vulnerable to cyber attack.
Microsoft said it will be providing security support for three more years to businesses using Windows 7 and for customers who are willing to pay for an upgraded package of updates.
However, the company itself warned users they would be at greater risk of hacking malware if they continued to use Windows 7 after Tuesday.
A Microsoft spokesman said: If you continue to use an unsupported version of Windows, your PC will still work, but it will become more vulnerable to security risks and viruses.