A scheme like this is easily circumvented with a firewall.

Maybe I'm a little paranoid, but my firewall is set such that
permission for any kind of network access is asked for any new app.
Apps that have no valid reason to access the network get a permanent
block.

Another Lee

> That idea is fairly similar to the idea someone on an ASP
> (Association of Shareware Professionals) forum suggested, which is to
> send out a multicast UDP packet on startup, that other instances of
> my program on the same subnet respond to with "Yes, I'm here". The
> sender counts the responses, and if they exceed the licensed # of
> users (minus one, to allow the sender to run), prevents the sender
> from running.
>
> This actually seems a bit simpler, because it doesn't need a server
> program, and isn't affected by crashes.
>
> Any comments on that idea? Thanks.
>