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Windows Defender Bug Could Be Slowing Down Your PC

The pre-installed antivirus tool is reportedly reducing Intel CPU performance by 6%.

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Windows Defender
Windows Defender
Photo: monticello (Shutterstock)

Your Intel-powered PC might not be running at full speed right now, and you can blame Windows Defender, the anti-malware tool that is preinstalled on your system. A bug, discovered by TechPowerUp associate software author Kevin Glynn, causes Windows Defender to “randomly start using all seven hardware performance counters provided by Intel Core processors.” A utility Glynn created that monitors and logs performance counters on Intel Core CPUs since 2008 found that the strange behavior results in significantly reduced performance.

Bogged down by Defender hogging CPU time, a Core i9-10850K running at 5GHz loses 1,000 Cinebench points, which is about a 6% drop from the norm. Owners with Intel Core 8th, 9th, 10th, and 11th Gen processors, on both desktops and laptops, have noted similar performance hits. AMD processors are not affected by the bug and some users report that 12th Gen Intel chips are also protected. We have not independently verified those claims.


As TechPowerUp notes, the underlying problem is that Windows Defender will randomly start using all seven hardware performance counters, including three fixed-function ones. Each counter can be programmed to a different privilege mode and is shared among multiple programs. For whatever reason, Defender is randomly changing the privilege level of the counters, creating a conflict with the programs trying to use them at a different level. It can happen at boot and sporadically thereafter.

To be clear, this is not an issue with Intel processors, because manually overriding the counters and resetting them returns a system to normal performance. There is no way to prevent Windows Defender from harassing your Intel processor unless you download third-party software. You probably won’t even know your CPU is being bogged down unless you’re actively monitoring its performance.


How do I stop this Windows Defender bug from slowing down my Intel CPU?

You could theoretically disable Windows Defender, but we don’t recommend doing so, as the security gains the program gives you outweigh these performance knocks. Another way of overcoming this bug is by downloading software created by Glynn called Counter Control, which identifies when Defender starts using all seven performance counters and “resets” them to their appropriate state.

A more permanent solution is to download TechPowerUp’s ThrottleStop v9.5 software and enable a feature called “Windows Defender Boost” in “Options.” This setting activates a programmable timer that Defender sees and reacts to by ceasing to use all the counters.

We have reached out to Microsoft for comment and will update this article. Hopefully, the company is aware of this problem and actively working on a solution so you don’t have to choose between performance and security.