Microsoft Defender, the security tool formerly known as Windows Defender (opens in new tab), received a new feature yesterday with the release of Tamper Protection (opens in new tab), which Microsoft started testing in December 2018. Now, Tamper Protection is enabled by default, though it can still be disabled by going into the Windows Security page in the Settings app.
So what does Tamper Protection do? It stops anyone without the proper authorization from changing Microsoft Defender settings to undermine Windows 10's security. For most people that's supposed to stop malware from making them vulnerable to other attacks, but Microsoft's enterprise customers can also use the feature to stop non-administrators from weakening a system's defenses.
Tamper Protection technically debuted with the Windows 10 May 2019 Update, but it had to be manually activated and was originally available only to certain users. Making it available to everyone running the most recent version of Windows 10 (opens in new tab) (the second annual update won't debut until November) and enabling it by default should greatly increase the number of systems protected by the new feature.
Microsoft said in yesterday's announcement that it "will continue working on this feature, including building support for older Windows versions," moving forward. In the meantime, it believes that "it’s critical for customers, across home users and commercial customers, to turn on tamper protection to ensure that essential security solutions are not circumvented."