Microsoft has dropped support for Windows 7 on a range of PCs dating back to turn of the millennium.

PCs whose processors lack support for multimedia instructions called SSE2 will no longer receive security updates for Windows 7, Microsoft has confirmed.

The issue first arose in March this year, when Microsoft issued a security update, (KB4088875), which generated a stop error on computers that didn’t support SSE2.

While Microsoft initially indicated it was working to resolve the error on Windows 7 machines, it later changed its advice, telling owners of affected PCs to “upgrade your machines with a processor that supports SSE2 or virtualize those machines”.

The result is that cumulative Windows 7 patches won’t install on PCs lacking SSE2 support from the March update onwards. Those who want to continue using Windows 7 on such machines will have to risk using PCs unpatched against the latest security threats.

Windows 7 was sold with the condition that security updates would continue to be issued until January 2020. But TechRepublic’s sister site ZDNet points out that Microsoft is entitled to make such a change under its Business, Developer and Desktop Operating Systems Policy, which states: “Older products may not meet today’s more demanding security requirements. Microsoft may be unable to provide security updates for older products”.

CPUs have supported SSE2 since 2000, with the multimedia instructions having been commonplace in processors since 2004 — meaning you’re unlikely to be affected unless you’ve held on to a Pentium III-era machine.

Last year Microsoft confirmed that laptops running on Intel Atom Clover Trail chipsets will not receive any Windows 10’s feature updates after the Anniversary Update, issued in summer last year.