Cory - this idea is a double edged sword. Keep in mind that it doesn't actually provide *service* to NATted boxen - it just counts them.

This means that your cable or DSL ISP can decide to charge based on the number of computers you have attached to your gateway.

The technique is not perfect - it's more like a heuristic, and depending on how implementations work, it might even count virtual machines (VMware) as additional systems.

On top of that - the article points out that this is only possible because most NAT points don't do their job correctly. The field they are checking in the packets is coming direclty from each system and is supposed to be unique in certain cases. Unless the NAT gateway rewrites the field, the uniqueness may fail if two systems are looking at the same destination at the same time.

In other words - this is possible because of a bug in most NAT routers.

I also suggested a cheap method of breaking up the pattern so that the heuristic will fail most of the time.