I can just agree with some of the previous posts, not to remove external modules usage. From my opinion there are enought security issues in every software and I guess, that this is the case in G2O too. So if someone wants to harm your computer, this will not only be possible via external modules but via Client-Squirrel-scripts or any "hacking-way".
So I recommend to just follow the way Julian suggested, to warn the user if a server uses external modules and that those can be a security lack.
Additionally you could add a kind of "server reputation" - feature, where players can give a positive or negative (Like or Dislike) reputation to a server which is shown in the server browser. According to Francis Galton and his experiments about the intelligence of a crowd of people and statistics those servers with many positive and only some negative reputation points will be servers the player can trust.
So I recommend to just follow the way Julian suggested, to warn the user if a server uses external modules and that those can be a security lack.
Additionally you could add a kind of "server reputation" - feature, where players can give a positive or negative (Like or Dislike) reputation to a server which is shown in the server browser. According to Francis Galton and his experiments about the intelligence of a crowd of people and statistics those servers with many positive and only some negative reputation points will be servers the player can trust.