- Report this to the registrar
- Report this to the DNS service they are using
- Redirect all incoming requests from that domain name to a page or another website.
It sounds like you've done 1. Action 2 may result in a better response - technically the registrar can do little. You'll want to read the terms of service for both 1 and 2, and find out if there's anything specific that they are doing to violate the ToS. Point this out, but be brief and to the point, "Your client, the owner of domain
example.com, is using DNS to direct traffic to my web server in violation of your terms of service, section 3.2 'You must not use this service to attack any website or internet service or user directly or indirectly'. Please consider disabling their account until they are in compliance with your Terms of Service."
For action 3 the specific implementation depends on your server. When a web client requests your site's homepage, it reports the domain name it intended to contact to your server.
In general, there are two methods to handle this:
- Your server may be able to be configured to reject or redirect requests for domain names. If you're using an Apache server, you'll need to edit htaccess, if IIS, you'll need to edit web.config. For other server types, try an internet search for "domain redirect [myservertype] rule".