It seems our approach with serial numbers (registration keys) appears to be quite efficient. So far at least. Thousands of legitimate installations around the world and only a few episodes of unauthorized usage (that we are aware of, of course).

Mostly from ex-USSR by the way.

IP: 83.146.79.xxx
IP location: Russian Federation [RU] - Chelyabinsk
IP owner: Southern Urals TransTelecom
IP assigned to: Southern Urals TransTelecom

This guy generated serial number with keygen quite some time ago. I believe he paid for keygen because I only know it is offered for money from a Ukrainian hack team. And I see he DOES have troubles with his unauthorized copy now. He is reinstalling it all the time trying to get it work, upgrading to newer versions and downgrading to older with little luck. In fact he have to finish downgrading to 1 year old release where protection from unauthorized usage was not improved yet. Or purchase legit license, but it does not seem to be an option for him :)