When an organisation has multiple branches where different user channel can access Salesforce, it’s only common the sharing settings for User is set to private. This will help to prevent a user from viewing another user.
However, there is one setting that needs to be considered when making user access private – Group tasks. This feature in enabled by default in Salesforce to allow assigning tasks to groups – role and subordinates/public groups as shown below.
Disabling this feature helps mask and not expose the list of roles to the users. Simply navigate to Setup > Activities Setting > (uncheck group tasks) to turn off this feature.