I've been using Terminus for about a decade and you can rip it from cold, RSI'd hands.

Send them a DMCA takedown notice. Under US law, the author retains copyright *even if that work was commissioned by someone else*. Most contracts therefore have a "work-for-hire" clause stating that rights will be transferred to client... but that won't apply if client hasn't met his end of the contract (i.e., paid).

If the risk of ridiculous punitive damages for infringement doesn't get their attention, send a takedown notice to the client's ISP/hosting provider (with proof of your copyright). The ISP is *legally obligated* to take the infringing content offline (i.e., the client's site) else they incur liability too. If that doesn't get you paid, short the client's stock, they're on their way out of business.

IANAL, YMM, who said copyright was all bad?

This is much the same point Jean Baudrillard made in Simulacra and Simulation. You may remember that book from cameo appearances in films such as The Matrix.

I happen to agree with both of them...