Legal Question in Technology Law in California

Re: Website violating Terms of Service

1) Actions in CA:

You can cancel their accounts (self-understood).

Most likely you will be able to sue them in California. It would be helpful if your terms and conditions had a venue clause in this regard.

In general California courts are willing to hear

cases of California citizens against the bad guys somewhere in the world.

You did not mention enough facts to assume that you

can send their ISP a DMCA takedown notice (for violation of your copyrights).

2) Actions at domicile of foreign violator

Once you have a California verdict (maybe even with damages) you can try to enforce it in the foreign jurisdiction. Countries in Western Europe have a comparatively reliable legal system one could use. (These countries consider the American legal system as messy and will not necessarily enforce all parts of the judgment).

You can of course try to sue the violator directly, however, litigation from afar is not that easy.

In general, litigation will cost you and might not be the appropriate measure against someone creating false accounts. Unless your business is seriously affected (and the violator is not just a nuisance) you might be better off taking technical measures against them