Most people said goodbye to Windows XP a long time ago. But if, for whatever reason, you're still running the out-of-date operating system, you really need to upgrade. Microsoft on Tuesday finally stopped providing antimalware signatures for Windows XP.

PCs running Windows XP have not been truly protected for more than a year. Microsoft on April 8, 2014 officially ended support for XP, meaning it stopped rolling out security updates for the aging OS. At that time, Redmond also stopped letting those on Windows XP download its Security Essentials tool, which guards against viruses, spyware, and other malicious software.

The software giant did, however, throw a bone to XP users who already had Microsoft Security Essentials installed, promising to keep it updated for a "limited time" to give people some more time to transition to a newer and fully supported OS. That time has now come and gone.

On Tuesday, Microsoft officially stopped providing updates to Microsoft Security Essentials for XP. Worse yet, XP users can no longer use Microsoft's Malicious Software Removal tool, so if your PC gets infected with malware — and it probably will — you're on your own.

For the tech-savvy, this is a non-issue. You've said goodbye to XP, which first launched in 2001, and embraced a more modern OS, like Windows 7 or Windows 8.

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Microsoft has been pleading with customers to upgrade to a new OS for years, so you can't say you weren't warned about this. If you're still on XP, perhaps now is a good time to finally upgrade. Windows 10 arrives on July 29.

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