Windows: Wrongly Hidden "Protected Operating System" Files and Folders

I came across an issue where a folder of SQL backups had been wrongly marked as hidden. They had been classed as "Protected Operating System Files" and so the "hide" box in the properties was greyed out.

Running the below from the command line removes the Hidden and System properties from the folder as well as from all sub-folders inside the top level.

attrib -H -S C:\path\to\your\folder /S /D 

or 

attrib -H -S C:\path\to\your\file.doc /S /D