Why is Apple showing a malicious software error when trying to install "Apple RehabStudio Installer.pkg"
“Apple RehabStudio Installer.pkg” can’t be opened because Apple cannot check it for malicious software.
[Re-Titled by Moderator]
If you’re certain that an app that you want to open is from a trustworthy source and hasn’t been tampered with, you might be able to temporarily override your Mac security settings to open it.*
For those directions, read down thru > Safely open apps on your Mac - Apple Support