The user will be prompted for a password in two situations:
You can control if you want this check enabled for all Revit family files or not as follows:
After the password is successfully entered, the user will not be prompted again for the password during that Revit session. If you purchase a license, a custom password can be set in the pwd.txt file in the BoostYourBIM-FamilySecurity.bundle\Contents folder.
NOTE: This app only protects families when this app is installed. There is no protection when someone without this app attempts to modify families.