Probably old news but here's an interview with a link spammer . I find his legal justification interesting:
Using proxy servers, Sam argues, is legal. (There seems to be some confirmation of this: you're not altering the machine's configuration, which would be illegal under the Computer Misuse Act, you're just using it to do something.) Sending viruses and using bots is not. "As well as being illegal, how much email spam gets through? The big link spammers, and me, we don't want to end up sharing a cell with a 300-pound guy called 'Bubba'. The moral argument, of whether this is the 'right' thing to do, is for the individual," says Sam. "The legal question is another matter."