What it checks
Gatekeeper is a macOS protection applied when an app, plug-in or installer from outside the App Store is opened. Apple describes checks for an identified developer's signature, notarization where required and signs of alteration. The warning is especially relevant when software arrived from a search result, unsolicited message or imitation vendor page.
A practical example
You download a familiar-looking utility from a search advertisement and macOS says the developer cannot be verified. Clicking Open Anyway would override a useful signal without proving the file's origin. Instead, find the developer's official site independently and compare its current download and installation instructions. A legitimate app may have a reason for a warning, but that reason needs evidence.
The limit
Gatekeeper cannot certify that every signed app will behave well forever. Apple says notarization checks for known malicious content at review time. Its
safe-opening guide describes the protection and narrow override. Treat the warning as part of a source-verification workflow; do not disable macOS security broadly just to get one installer to run.
