Microsoft has responded to complaints by Kaspersky Lab that it uses "underhand tactics" to remove third-party antivirus.
Kaspersky Lab in June took its complaints over Windows 10's handling of third-party antivirus to the European Commission and the German Federal Cartel Office.
One of the key complaints is that Windows 10 uninstalls Kaspersky antivirus without the consent of users and enables the built-in Windows Defender.
Kaspersky argued the switch happens during major Windows updates if a third-party AV product is incompatible with the latest version of Windows.
Now Microsoft has responded more fully to Kaspersky's complaints, arguing that it's been actively helping antivirus vendors.
But the new blogpost by Rob Lefferts, Microsoft's partner director of the Windows & Devices Group, Security & Enterprise, also admits that Windows 10 Creators Update did disable third-party antivirus products, although only for a short time.
"We built a feature just for AV apps [pictured above] that would prompt the customer to install a new version of their AV app right after the update completed. To do this, we first temporarily disabled some parts of the AV software when the update began," wrote Lefferts.
"We did this work in partnership with the AV partner to specify which versions of their software are compatible and where to direct customers after updating."
Kaspersky founder Eugene Kaspersky has accused Microsoft of using shady methods to "fiercely promote its own inferior" product, Windows Defender, over third-party antivirus already installed on Windows 10 PCs.
The Russian antivirus firm also filed a complaint with Russia's Federal Antimonopoly Service over the same issues last year, which resulted in some changes by Microsoft, but not enough, apparently.
He's also complained that AV vendors have little time to make their product compatible, compared with previous versions of Windows. Other vendors, like ESET, cited similar compatibility problems with the Windows 10 Anniversary Update.
So far Microsoft hasn't commented much on the complaints beyond saying it is confident Windows 10 security features do comply with competition laws. But Lefferts' blogpost on Tuesday, which doesn't mention Kaspersky, addresses many of the security vendor's criticisms.
He said the threat of ransomware, such as the recent WannaCry outbreak, meant it has a duty to ensure some malware protection is "always on", regardless of the system users choose.
"Only when an AV subscription expires, and the AV application decides to stop providing protection to the customer, will Windows Defender Antivirus begin providing protection," explained Lefferts.
Lefferts also notes that Microsoft "doubled down" on efforts to help AV vendors stay compatible with the Windows 10 Creators Update, arguing that nearly all antivirus applications Microsoft tested are fully compatible.
"Microsoft's application compatibility teams found that roughly 95 percent of Windows 10 PCs had an antivirus application installed that was already compatible with Windows 10 Creators Update," said Lefferts.
Other complaints from Kaspersky include Microsoft brochures stating that Windows users don't need to pay for third-party antivirus because of Windows Defender, that Windows Defender runs duplicate malware scans, and that Microsoft's tech support staff have advised users to uninstall Kaspersky.
Lefferts denied all these claims, insisting Microsoft believes in supporting a diverse security ecosystem.
"Once a customer has installed an active and up-to-date antivirus program, it will run without notifications or interference from Windows. Microsoft's own free, built-in Windows Defender Antivirus does not run periodic scans without explicit customer action or provide protection until the chosen third-party AV solution is no longer protecting the Windows 10 device due to expiration," said Lefferts.
"When customers experience support issues, our Microsoft Support teams work closely with them to honor the AV choices they've made. In some cases, uninstalling and then reinstalling the software, including third-party AV solutions, is a necessary step in resolving a customer issue."
Finally, Lefferts countered Kaspersky's claim that Windows Defender is an inferior product, pointing to AV-Comparitive tests that show it neck and neck with top performers, including Avast, AVG, BitDefender, BullGuard, F-Secure, Kaspersky, and Trend Micro.