This is the bug appeared after the “Defender” was updated to version 1.353.1874.0. Thus, Microsoft Defender blocks the opening of files and issues a warning about suspicious activity related to Win32/PowEmotet.SB or Win32/PowEmotet.SC. Some administrators were unable to open Excel documents and cited the upgrade to version 1.353.1874.0 as the reason:
FIx is to update the machines latest Definition 1.353.1874.1888.