Microsoft suddenly issues chilling warningSOPA Images/LightRocket via Getty ImagesMicrosoft has suddenly issued its most chilling warning yet for 800 million Windows users yet to upgrade to Windows 11. If there was any doubt as to its resolve to hold a firm line on ending Windows 10 support, thats gone. All those PCs will be wide open to data breaches, identity theft, and other serious consequences, it warns. Not fun.This week many Windows 10 users have already received an email telling them to check the upgrade eligibility of their PCs or look into buying a new machine. When your OS is no longer getting those all-important security updates, it can be a bit like leaving your front door wide open, it says, spelling out just what could happen if you dont.The Windows-maker warns those 800 million users (per Statcounters latest numbers) will risk increased vulnerability to malware, as well as risk of cyberattacks. Microsoft has confirmed a 12-month extended support option will be available for $30. But just as with its emails this week, this doesnt feature. The company likely doesnt want that to be a large-scale fallback or it doesnt think huge numbers will pay.Security updates, it says, are like locks on your doors they help keep the bad guys out. And coming just a few days after its latest monthly update warnings of yet more zero-day vulnerabilities under attack, it stresses that these updates patch up vulnerabilities that could be exploited by malware or hackers. Without them, your unsupported OS is an easy target, and your personal info could be at risk.The nightmare scenario of hundreds of millions of PCs all falling off support on October 14 is certain to be exploited. Cybercriminals are a crafty bunch, and theyre always on the lookout for outdated systems to exploit. An unsupported OS is like an open invitation for these attackers. Once theyre in, they can steal sensitive information, install ransomware, or use your system for their own nefarious purposes.Microsoft has pushed the benefits of Windows 11 hard, the combination of its new OS and newer hardware delivering a step-up in security benefits. But the tone of this latest warning is likely what well see for the next seven months, as the end-of-life deadline comes closer. Microsoft isnt wrong the risks for PC owners staying put are huge.Using an unsupported operating system is a risky business that can lead to serious security issues. The upgrade to Windows 11 is free for eligible PCs running fully-licensed Windows 10. That upgrade, Microsoft says, can protect your device and personal information from malware and cyberattacks. Dont wait until its too latemake the switch today and enjoy peace of mind knowing your digital life is secure.