In SQL Server, a list of all the users has been created by the tool. Unknown and Empty are the two values which was carried out by password column.
Unknown means that you have a password presently but is encrypted.
Empty stands that no password and you can login to their account without password.
Now take Attention: Further take a step it is highly recommended to take a backup of your Master .mdf and Master_log .ldf files as the tool will make changes to your Master database in the next step.