Windows 7 users have been warned to upgrade their PCs to avoid possible cyber attacks as support for the software ends.
From Tuesday the 10-year-old operating system will no longer receive critical updates, meaning Microsoft will stop patching any weaknesses that appear.
PCs will ultimately become vulnerable to hacker attacks.
Windows 7 is still one of the most popular Windows operating systems with a 32.74% global share, according to NetMarketShare estimations.
It is second only to Microsoft’s most recent version, Windows 10, at 47.65%.
GCHQ’s National Cyber Security Centre (NCSC) has warned the public not to access banking, emails or other services containing sensitive information from devices on Windows 7 due to the high risk.
End of support is a long-running measure by Microsoft as it moves from dated technologies and increases focus on newer ones.
An NCSC spokesman 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.”
Affected computers will remain functional but will no longer be secure.
Companies which are not ready for the move can choose to pay Microsoft for extended security updates through to January 2023.
However it is sold on a per-device basis and the price will increase each year in a bid to encourage businesses to upgrade.