PC users running Windows 7 have been warned to upgrade to avoid possible cyber attacks as support for the software comes to an end.

From today, the ten-year-old operating system will no longer receive critical updates, meaning Microsoft will stop patching any weaknesses that appear, making machines vulnerable to hacker attacks.

It is estimated Windows 7 is still one of the most popular Windows operating systems in use, with nearly a 33% global share, second only to Microsoft's most recent version, Windows 10.

It is thought around a fifth of PCs running on the Windows platform in Ireland use it.

Microsoft has been warning for the past five years that it would end support for the product, as it shifts its focus from old technologies and puts its resources into newer ones.

Computers running Windows 7 will remain functional, but will no longer be completely secure, as they will not receive updates or patches from Microsoft.

Companies and organisations that are still not ready for the move can choose to pay Microsoft for extended security updates for the next three years, though it is sold on a per-device basis and the price will increase each year.

Thousands of computers in the country's public service are still reliant on Windows 7, including 46,000 of the 58,000 PCs in the HSE.

It will spend over €1m on extended support from Microsoft for the operating system this year, as it continues the process of upgrading its computers.