Where do you report "free" servers?

Is there such an option? I got invited to join one of the "free" servers, but I'm pretty anti-stealing and don't like that people aren't paying for a game that I love so much I bought several copies. I know Blizzard has taken action in the past against free servers, but I didn't know if there's still a way to report them. Any ideas?

Please don't let this devolve into a huge "it's not stealing" argument. People are taking intellectual property they didn't create and allowing others to use it without paying for it (or, in some cases, paying for it but without that money going to the people involved in its production). We all cough up 15 bucks a month in appreciation of the game Blizzard has made, let's just leave it at that.