This is a feature of SEP. This happened because SEP found that a threat was trying to hijack your browser homepage so SEP changed your homepage to let you know. This can option can be found in the AV policy under the MIscellaneous tabe, please see here:
About Symantec Endpoint Protection's Internet Browser Protection
Now, please run a full scan with SEP and also run a threat analysis scan using the symhelp tool.
How to run the Threat Analysis Scan in Symantec Help (SymHelp)
If neither of these work then run the norton power eraser found here:
https://security.symantec.com/nbrt/npe.aspx?
As a last resort, you can run a tool called AdwCleaner which also does a nice job of removing hijacking threats.
Let me know if you have any further questions.
Brian