Some Windows 11 users cannot update the Microsoft Defender

Some Windows 11 users are running into a problem with Microsoft Defender. Reports from ITHome say that people using Windows 11 24H2 noticed their virus definitions haven’t updated since November 19, 2025. This is trying to say that their computers might have been open to new viruses and threats.

The confusing part is that Defender doesn’t tell you anything’s wrong. Most people only notice something is wrong when they open Windows Security, go to Virus & threat protection updates, and click Check for updates. That’s when they realise the virus definitions haven’t changed.

Even though Windows tells you “You’re using the latest version”, the last updated date is a few days old. That makes it easy for regular users to think everything is fine when it’s not.

The author of the blog tried this on a Windows 11 25H2 Pro virtual machine. On that system, the updates went through without any real problems, and it successfully installed the latest Security Intelligence Update, version 1.441.473.0, on November 25, 2025. But there was a small glitch along the way. Windows Security briefly showed a message saying, “Threat service has stopped, please restart immediately.” The service quickly restarted on its own and continued updating. It seems that updates generally work, but the Defender service can be a bit unreliable at times.

Many users won’t even realise there’s a problem unless they check by hand. But being stuck on old virus definitions can leave your computer at risk. Microsoft hasn’t said anything about the issue yet, and it’s not clear how many Windows 11 users are affected.

Defender still works, but it’s a good idea to check your updates now and then. Look at the last updated date in Windows Security to make sure your definitions are current. If you see any warning messages about the service stopping, pay attention; they could signal update problems. Staying on top of this helps keep your system safe.