The autoblock has nothing to do with the CheckUser tool Any time you attempt to edit from a blocked account the IP address used gets blocked with something called an autoblock These special blocks appear in the block log with a number not an IP address but some times a request to unblock it is made and that reveals the address I don t believe that Luna Santin ran a CU without a valid reason He isn t required to reveal his reason on wiki although given the recent problems on this IP address from someone called I m not surprised There is nothing illegal about CU which is done without revealing the information to the public There is nothing illegal about the autoblock it only reveals the IP address to the general public if someone on the same IP address chooses to do so Checkuser blocks are done in a way which protects the blocked user from having his IP address revealed to the public as much as possible I think you should read the privacy policy Please note that making legal threats is itself a good enough reason to block this IP address for a few months