I activated ZBrush several times, once even without internet connection. I had to call a service. But it always works fine.

By the way. The latest version asks for a description of your machine you are using. So you can write "Desktop at home", "laptop" and so on. So they will see that you are the user and how you use it and that you use it on desktop plus laptop.
I find this ok. There are lots of warez copies of ZBrush and I would be happy if they find a way to stop this. If these warez guys have no money then they can work and sculpt freely with Blender.