You have sent him probably a slightly different labview version, so it need to be compiled on his machine and that is not possible without a diagram.
Password protection is failsafe enough.
It takes much longer to crack a password than to develop a new vi that has the same functionality. Especially when the pasword contains a mix of letters, numbers and other idiot signs. Using a belgium keyboard makes it even better possible to generate a crazy password. In the Netehrlands we need to press shift for the @#$%^&* ect keys.
greetings from the Netherlands