I'm trying to decide how to implement a very basic licensing solution for some software I wrote. The software will run on my (hypothetical) clients' machines, with the idea being that the software will immediately quit (with a friendly message) if the client is running it on greater-than-n machines (n being the number of licenses they have purchased). Additionally, the clients are non-tech-savvy to the point where "basic" is good enough.

Here is my current design, but given that I have little to no experience in the topic, I wanted to ask SO before I started any development on it:

• A remote server hosts a MySQL database with a table containing two columns: client-key and license quantity
• The client-side application connects to the MySQL database on startup, offering it's client-key that I've put into a properties file packaged into the distribution (I would create a new distribution for each new client)
• Chances are, I'll need a second table to store validation history, so that with some short logic, the software can decide if it can be run on a given machine (maybe a sliding window of n machines using the software per 24 hours)
• If the software cannot establish a connection to the MySQL database, or decides that it's over the n allowed machines per day, it closes
• The connection info for the remote server hosting the MySQL database should be hard-coded into the app? (That sounds like a bad idea, but otherwise they could point it to some other always-validates-to-success server)

I think that about covers my initial design. The intent being that while it certainly isn't full-proof, I think I've made it at least somewhat difficult to create an easily-sharable cracking solution. Also, I can easily adjust the license amount for a given client/key pair.

I gotta figure this has been done a million times before, so tell me about a better solution that's just as simple to implement and provides the same (low) amount of security. In the event that external libraries are used, I prefer Java, as that's what the software has been written in.