When trying to open an Excel file, you may run into the following error:

"The file you are trying to open, [filename], is in a different format than specified by the file extension. Verify that the file is not corrupted and is from a trustworthy source before opening the file. Do you want to open the file now?"

Clicking Yes to open the file, you may find that the content of the file is unreadable and contains unreadable characters and/or symbols.

This is an issue that can happen when Symantec Endpoint Protection is installed on the machine. To resolve the problem, update Symantec Endpoint Protection to the most recent version.