That’s the advice coming from the U.S. Computer Emergency Readiness Team (US-CERT), following an “urgent call to action” by cybersecurity firm Trend Micro(TMICF). The version of QuickTime on Apple(AAPL) computers is not affected.

What’s the rush? Trend Micro found two critical flaws in the PC version of Apple’s media-playing software that could let hackers take over victims’ computers.

Get Data Sheet, Fortune’s technology newsletter.

And is Apple fixing the flaws? Nope. According to Trend Micro, after the security firm advised Apple about the vulnerabilities back in March, Apple waited four months before telling Trend Micro that it would simply stop supporting QuickTime for Microsoft’s(MSFT) Windows, and give users instructions for how to remove it.

So here are those instructions. If you have that software on your PC, you know what to do.

“We’re not aware of any active attacks against these vulnerabilities currently. But the only way to protect your Windows systems from potential attacks against these or other vulnerabilities in Apple QuickTime now is to uninstall it,” wrote Trend Micro’s Christopher Budd in the advisory.

For more on Apple, watch:

Apple last issued a security patch for QuickTime for Windows on January 7, but it clearly didn’t fix the flaws in question.

It’s not normal for a company of Apple’s scale to not warn customers of its intention to drop support for software, particularly very widely-used software that’s been around for over two decades. Sure, QuickTime isn’t the best media-playing software available for Windows, but a lot of people install it bundled with iTunes.

Fortune asked Apple if it had intended to give users a heads-up, but the company declined to give a statement on the matter.