What is the oldest version of SEP that can run on Windows 8.1?
SEP 12.1.4 (RU4)
About Windows 8 and Symantec Endpoint Protection 12.1
Note: Windows 8.1 is only supported with Symantec Endpoint Protection 12.1 RU4 and later.
SEP 12.1 RU4 is the version that is supported on windows 8.1
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Expanded operating system and browser support
Supports Mac OS X 10.9 and Windows 8.1 / Server 2012 R2.
Supports the latest versions of Internet Explorer, Firefox, and Chrome.