Surely this should be either deactivated or banned.
However, a small technical info: the master servers are just providing a list of ip adresses, the individual information is sent from the individual server to you directly.
Now that I'm thinking about it, I don't know who invented that but actually this is a pretty major privacy issue.
1. The ip address of everyone who queries the serverlist is sent to everyone on the serverlist
2. This extends even farther with custom clients which trigger automatic serverlist reloads.
=> this might be exploited by placing fake server entries in the master server list, querying the serverlist on said server frequently and mapping incoming request ip addresses to users when it is likely that a certain user is right now querying the serverlist. Over some time a database could be built linking players to ip addresses with a certain probability which depends mainly on the amount of recent playtime, which can be used for attacks on an individual but also "just" tracking players across servers and even across name changes in many instances, all without a player ever consciously connecting to your server. A demonstration of this attack is yet outstanding but that doesn't have to stay this way.
Having troubles finding servers in the serverlist? Go to
Pastebin (its a referer cause there is daily a new pastebin) and add the lines to your settings.cfg (in %APPDATA%\teeworlds). Then open teeworlds and go to the favorites tab. (Note however, standard teeworlds client can only show 256 favorites, use ddnet instead)