Microsoft Defender May Hurt Performance

John Lister's picture

Microsoft Defender has come in last in two separate tests of Windows 11 security software. It's a surprise result given it generally did well on Windows 10.

There's some comfort for Microsoft, however, as the nature of the testing means many users won't notice that much difference in practice. That's important given Microsoft Defender (previously Windows Defender) is built-in to Windows 11.

The first rankings came from AV-Test, which describes itself as "The Independent IT-Security Institute." It ran a series of tests on 19 products using "realistic test scenarios" and "real-world threats." (Source:

Each product was given scores out of six for three categories: protection, performance and usability. Microsoft Defender got the full score for usability. It also got 5.5 for protection, picking up 98.8 percent of zero-day attacks and 100 percent of "widespread and prevalent malware." However, Defender only got 4.5 for usability, based mainly on it slowing down the copying of files.

The overall score of 16 out of 18 put it in joint-last place and meant it missed out on a "Top Product" rating. However, it easily cleared the bar of 10 points to get AV-Test's seal of approval, meaning its worth using.

Performance Slowed

Defender also did poorly on a test run by another organization, AV-Comparatives. It wasn't judging how effective the security tools were at detecting viruses, but rather it specifically looked at the effect on system performance. (Source:

It times how long a variety of common computing activities took while running each security tool. These included copying files, using archive tools such as ZIP files, installing applications and browsing websites.

The organization then turned the results into an "impact score" where the bigger the score, the more the tool affected performance. While 13 of the 17 tested tools had a single-figure score, Microsoft Defender was in last place with 27.7 points.

Effect Hard To Compare

Across the two tests, the common theme is that Defender does a perfectly fine job of detecting and dealing with security threats and its main weakness is that it slows down various computer operations – at least in comparison to rival tools.

That's where being the default security tool in Windows is a major advantage. Even if the performance impact would be noticeable compared with running a rival tool (or no security software at all), that's not a comparison most people will make.

Instead the speed which Windows 11 performs various tasks while running Microsoft Defender is simply what many users will experience as "normal".

What's Your Opinion?

Do you use security tools other than Microsoft Defender? Have you ever uninstalled or disabled an operating system's built-in security tools? If you've upgraded to Windows 11, have you noticed any key functions feeling slow?

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LouisianaJoe's picture

The average user has no clue about performance. Since Defender is part of the OS, they do not have to buy anything and they do not have to install anything. They have no idea what makes another product better. I have been programming for over 55 years and I no longer care about incremental improvements.

matt_2058's picture

When I bootup or restart my laptop using the included tools, it's useless for 5-10 minutes because the scans begin right out of the gate. I start Task Manager and wait until the pegged memory and disk usage goes down before doing anything else.

That's a minor inconvenience. Years ago, my Govm't computer took about 30 minutes to be ready due to the scans and network scan BS. Back then they rotated using McAfee and Norton every other year or so.