Column Level Security (CLS) is a SharePoint hosted app which helps administrators apply column level security to SharePoint Lists and Libraries. Through CLS, you can hide columns for specific Users/Groups or make columns Read-only for specific Users/Groups per your business needs. This app works on web scope and needs to be installed on each web(site/subsite) as required.
While editing an existing form, Columns which are set with Read Only Permission, a user will not be able to modify those Columns’ data.
Whereas for Columns which are set as Hide, users will not be able to view the data for those Columns.
If hide permission is applied to any column for a set of Users and/or a Groups, then “Export to Excel” link in ribbon will be hidden for those Users/Groups.
If read or hide permission is applied on Attachment column, then “Attach file” ribbon button will be hidden for those Users/Groups.
SharePoint Online or SharePoint On-Premise 2013/2016
Microsoft Internet Explorer 10 or higher, latest version of Firefox and Chrome