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They can sometimes be harmful yeah. Disavow the domain in Google's disavow tool.  Remember to download the existing disavow file and add your new entries on, otherwise you might undo some previous work. The file you upload doesn't get 'added' to what you have submitted previously, whatever you upload IS the complete file (be wary) Other than that I'd just listen for any traffic from the domain and 301 redirect it somewhere else. The problem you'll get is that if you 301 it back to them, their redirect will pass back to you and you'll get an inter-domain redirect loop I don't know what the consequences of that are. You could just 301 redirect traffic and negative equity from that site, to someone you don't like no? Ok, maybe a bit too volatile and thermonuclear In all seriousness the best thing to do is disavow and code your server to refuse to serve anything to any requests processed from that domain (be they crawlers or users). Just shut it down and disavow it, that's what I'd do. Redirect-wars are seldom beneficial