This issue can occur during a migration or new installation of Symantec Endpoint Protection (SEP) 12.1 or 14 on a MacOS system.

Install fails during the pre-installation environment check with the following message:

"The selected drive already has security software installed that is incompatible with Symantec Endpoint Protection"

Operating System:

• Mac OS X (10.8 and later)
• MacOS Sierra (10.12 and later)

Symantec Endpoint Protection:

• SEP 12.1 RU6 and later
• SEP 14 and later

The SEP for Mac installer runs a pre-installation environment check that includes a check for third party security software.  These results can be viewed in the MacOS system.log file.

system.log location:

• system.log can be viewed by launching the Console utility.  
• system.log is located in the /private/var/log directory (to view hidden folders from Finder, click on Go > Go To Folder and enter the directory path).

Example of entry in system.log:

Month Day xx:xx:xx hostname Symantec Endpoint Protection Installer[PID]: ABC security is installed on the volume 

NOTE:
SEP may detect software that is no longer installed if the uninstall process left remnants on disk.  Since MacOS provides no default software removal mechanism, applications are often uninstalled by moving the application files from /Applications to Trash.  This is not sufficient for some applications, including those that are bundled with an uninstaller app.  One common location for additional files is the /Library/Application Support directory.

1. Remove the security software referenced in the system.log file.  If the referenced software is no longer available in the /Applications directory, check common locations such as /Library/Application Support or /Users/username/Applications or search for remnant files using the Find command in Terminal.
2. Complete migration or installation of SEP for Mac.