We're getting exactly the same issue. Started beginning of July and around 50 orders a day with no payment. Same domains as 'snake' mentions above.
Ideally I don't want an order or client being created if there is no payment made at the time. It takes a long time to go through and manually remove the spam clients.
I have "Allow Client Registration" disabled. All this did was make the spammers create fake orders instead of just fake client registrations.
Literally another two have just come in as I type this...
