Build control (serial key / licence ?)

Hello guys, I'm working in a big company and I created a tool based on Unity.
(I don't know if it's important, but the application is using the "StreamingAssets" folder to run and I would let this folder accessible)

The real thing is that we would like to deploy the application but with some controls other users.

At this point the application is pretty... "stealable". You just have to copy the build folder, and you've got the application. I'd avoid that as other companies could steal the application pretty easily.

- I first thought of a database (but what should I check to make sure it's ok ? Some computers might not be connected to the network... The firewall might also be a problem isn't it ?!)
- I spoke with some IT guys. I didn't understand much, but I think the goal was to check the existance of a serial key inside "root", with a setup in which there is the build of the application.
- I already saw someone sending me an .exe to make their application run, but I have no clue how it was done.

I'm sorry, I'm a bit confused, but if you have some ideas, recommandations, notions, I would really appreciate your sharing.
Thanks.