Actually there are a number of license management solutions that can help, but the REAL problem is that all of they can be cracked. I've personally tried the most expensive to the cheapest. Finally I rolled my own, and I check the software's pc details (mac id, etc.) against the recorded details in my server every time the software is run. Because my software is tightly tied to the Internet, it is okay, but I am sure it will be cracked one of these days.
What you probably need is to police the Internet regularly, and find where your software is being pirated, contrary to the popular belief you can actually stop them in most cases. Just serve a DMCA to the downloading website (most of them will comply), and you will be able to get your software removed in about 80% of the cases. I've done and experienced it on my software. Some people do not remove, but I've found that in the 1.5 years I've been doing this, my sales have improved.
I also use a service -- http://spotpiracy.com which helps me find these links apart from my own manual research (i have a guy dedicated to this). :)