MS veteran Raymond Chen, who has worked at the company for more than three decades, has straightforward advice for anyone using two or more antivirus solutions: Do not run multiple antivirus programs.

While helping a colleague investigate a complex system failure on Windows 11 Enterprise PCs, Chen discovered that two anti-malware programs were interfering with each other. One antivirus attempted to quarantine a process belonging to the other, which then successfully quarantined a process belonging to the first.

“Installing two anti-malware programs on the same system is like hiring two different security companies to patrol your building,” Chen argued, without specifically advocating for MS Defender.

“If they don’t know about each other, each is going to think the other one is an intruder. If you’re lucky, their instructions are merely to report on suspicious activity.”

MS says antivirus products are not like two security companies that can be introduced to each other, assigned to different floors, and expected to avoid conflict. These applications monitor all processes, and users cannot simply whitelist the processes used by another antivirus program.

“In software, this is harder to do. It’s not like you can invite two programs to lunch and have them get to know each other,” he added.

Antivirus Conflicts on Windows 11 Can Extend Beyond Mutual Quarantining

Another problem with third-party anti-malware software is that it may use techniques that are not officially supported or recommended, including “detouring system functions.” This can cause significant performance issues and other problems.

“These detours mean that calling a system function no longer does the system thing; instead, it calls into the anti-malware software, and it might decide to do something unrelated to the system function you thought you were calling, and that unrelated thing may itself start causing problems, say, by hanging,” Chen noted.

Running multiple antivirus programs invites trouble and may produce different Windows problems from one day to the next. MS Defender itself can be resource-intensive, and users may occasionally notice its anti-malware process consuming most of the CPU. Adding more antivirus applications to a Windows installation can make this problem worse.

Consumers cannot easily debug these issues or determine whether a third-party anti-malware program has interfered with Defender. As a result, they may blame a faulty Windows update for problems it did not cause.

In its tests, Windows Latest found that most of these issues could be traced through Event Viewer, although doing so can still be difficult for an average home user.

What should users do in this situation? MS’s advice is to avoid using a third-party antivirus program in the first place.

MS Previously Said Defender Was Sufficient for Most Users

In April 2026, MS published a support document describing Windows Defender, renamed MS Defender, as more than sufficient for most users and suggesting that a third-party antivirus program was generally unnecessary.

That claim was not entirely unfounded. Defender in 2026 is significantly different from the version available in the early 2000s.

MS also called Defender the “best antivirus software for 2026.” However, shortly after Windows Latest discovered the document, MS quietly removed the entire page. The company stopped publishing these recommendations in June 2026.

MS never explained why it stopped calling Defender the best antivirus software, although the marketing campaign may have attracted the attention of its partners.

Windows Latest captured a screenshot of the deleted document, which clearly shows MS declaring Defender the best antivirus software.

MS created this document not only to promote its own product, but also to rank Defender in searches for “best antivirus software” on Google, Bing, and large language models such as ChatGPT and Claude.

MS Explains Why Windows Defender Is More Than Sufficient

In the now-deleted document, MS confirmed that Windows 11 already includes an “antivirus stack” and listed several features that users can manage through the Windows Security app.

These include Defender Antivirus, the core engine; SmartScreen, which is enabled by default; and Smart App Control, which is typically disabled by default. Windows 11 also provides more advanced capabilities, including ransomware mitigation and the ability to block potentially unwanted applications.

“Windows antivirus protection is usually sufficient when Windows 11 runs with default protections enabled, updates are installed regularly, and software downloads are deliberate,” MS stated in the support document previously viewed by Windows Latest.

MS also argued that these Windows 11 features provide a “baseline” that covers most attack paths without requiring additional software.

The company also warned about performance concerns when more than one security application is installed:

“More than one real-time antivirus engine increases resource use and raises the chance of conflicts.”

I agree with MS’s assessment. Based on my experience with Windows over the past decade, Defender has improved noticeably, and I have not encountered any security incidents while it was enabled. Independent laboratories support these findings. AV-Test, an independent testing organization, ranks MS Defender among the leading antivirus products, with protection scores ranging from 98.5% to 100% in its benchmarks.

Do you use a third-party security solution on Windows 11? Share your experience in the comments below.

Windows Latest depends on readers like you. Make us your preferred source on Google Discover and Google Search, and help our independent reporting reach more people.