Why it matters: It's been almost five months since Windows 7 reached the end of its extended support period, meaning that the only users to receive extended security updates (ESUs) are businesses and education customers willing to pay for them. Despite this, the venerable OS is still the second most popular operating system behind Windows 10, taking a near 25 percent share of the market.

Hard as it is to believe, Windows 7 released way back in 2009. It exited mainstream support and entered its extended support phase in January 2015, allowing users to still receive free critical security patches, bug fixes, and technical support for the next five years.

On January 14 this year, the extended support period ended. ESUs are still available to all Windows 7 Professional and Windows 7 Enterprise customers, but Microsoft charges $25 (Enterprise) or $50 (Pro) per machine, and those prices go up every year.

With Windows 7 no longer receiving patches for newly discovered vulnerabilities, it's increasingly at risk from cyber attacks---the UK's National Cyber Security Center has warned people not to use Windows 7 for internet banking or even emails. But its number of users has barely changed since January, with the OS still found on almost a quarter of PCs (24.28 percent), according to NetMarketShare.

Twelve months ago, Windows 7 had a 35 percent share of the market, so a 10 percent drop for a decade-old OS that's no longer supported isn't bad at all. But why do so many want to avoid upgrading to Windows 10? A lot of it is due to privacy concerns surrounding the modern system, though Microsoft has done a lot to address this in recent times. There are also the numerous issues caused by Windows 10's updates, the fact that some businesses simply haven't got around to updating, and many people just prefer Windows 7.

Elsewhere, Windows 10 continued to cement its position at the top after increasing its share to 57.83 percent. In March, Microsoft finally reached its goal of one billion devices running its latest operating system, missing its original prediction by 20 months. And it's good news for Linux, which reached an all-time high of 3.17 percent.