Box.net allows you to password protect files you are sharing or sending to someone, requiring that user to enter the set password to access the shared file(s).

To set a password on a file or folder, right-click on on an item in your Box account and select 'Link to this File'



You will then see "Password protect this share" Click that and type the password you wish use. Then click 'Set this password'. To deactivate the password later, go back to this dialogue box and select 'Deactivate'.