Multiple registrations?

I'm a member of several English-language and German-language forums, but my favorites are TCS and a similar German-language forum (http://www.zooplus.de for the German-speakers here). The administrators of the latter are complaining about people registering under various Web names, and using their "aliases" to post controversial threads or insult other forum members. Anne, M.A, and other moderators here: Have you encountered this problem, and if so, how have you detected and dealt with it? I'd hate to see the other website shut down, because I've gotten a lot of advice about food, medications and treatments there that apply to Germany only. The administrators appear to be very apprehensive about lawsuits, and seem to be contemplating doing away with the website.

We are fortunate that the moderators here are on their toes, and ISP numbers are checked a lot when it comes to questionable posts. If indeed we find that someone is posting controversy on purpose to cause problems and is a registered member under another name, they are warned to stop. If they ignore the warning, other actions are taken including banning if it is deemed necessary.