Manage the Guest user account
Add extra security and lock things down.
Your Mac automatically creates a guest user account that doesn’t require a password. If you know you’ll never need it, the best option is to turn it off. Go to Users & Groups, click the Guest User and untick ‘Allow guests to log in to this computer’. This pane also lets you block guest access to shared folders. If you want to restrict guest access to certain apps, click Open Parental Controls, enter an administrator’s credentials and then choose whether you want to restrict the use of your Mac’s camera, apps, Mail and games.