This question already has an answer here:
A well-known crank, let's call him "Wolfgang", uses ten different sock-puppets to dump his pseudo-scientific nonsense into several Stack Exchange sites. Every time another user, let's call him "Uwe", notices Wolfgang's questions or answers, he adds a comment "Warning: "Forte" is one of Wolfgang's ten sock-puppets, and discussing with Wolfgang is known to be pointless". Then Wolfgang changes the display name of his sock-puppet "Forte" to "Uwe", which not only confuses other readers, but makes commenting quite difficult for Uwe. Is this considered as acceptable behaviour, or is it something that moderators (have to?) deal with?