(Since March 2021, Viewer is only supported on versions of Microsoft Windows supported by Microsoft.  Before March 2021, Viewer ran on Windows, Mac, and Linux.  At that time, we dropped support for Mac and Linux due to low demand. This article remains for those running unsupported versions.)
In some Mac environments, the Viewer installer may give a "broken" or "unidentified developer" warning. This is an indication that the installer has been quarantined by your system. There are 2 options to correct the issue.
First, instead of double-clicking on the file to open it, right-click on the file and select "Open". You might get a warning about it being from an unidentified developer, but this time you'll have an Open button and you should be able to get past the error.
If this does not solve the issue, from a command line, execute the following command:
$ xatttr -d com.apple.quarantine spv_2020_4_90_macos_setup.dmg
(where spv_2020_4_90_macos_set.dmg is the dmg you are installing)
Then, you will be able to run the installer.