Files from Internet zone must be opened in Excel in Protected View mode.
This policy setting allows you to determine if files downloaded from the Internet zone open in Protected View.
If you enable this policy setting, files downloaded from the Internet zone do not open in Protected View.
If you disable or do not configure this policy setting, files downloaded from the Internet zone open in Protected View.
How this relates to the STIG checklist: STIG vs SCAP benchmark.