How to block an anonymous troll other than by IP(s)?

Question

On our platform, we have the possibility to block registered users by user name or IP, whereas anonymous users can be blocked by IP only. Also, we have some kind of a reputation system such that only registered users can accumulate points, but commenting, asking, and answering does not need any points such that anonymous users can contribute too.

Now imagine that there is a malicious troll, who does not register on purpose and comes in by several different IPs. In principle he could be blocked by the say 10 IPs he uses, but this would bear the danger that as depending on the provider several costumers share the same IP, we would block almost the whole country the troll comes from.

So is there another solution to block such an anonymous user than by IP?

Our system development team has full controll over the software of our platform, we are not on Stack Exchange.

Answer 1

These ideas are drawn in large part from Stack Exchange and partly from anti-spam techniques.

Filtering

If there are patterns in the trolling, you could take a page from automated anti-spam measures and apply pattern-matching to the problem. This depends on how well you can characterize trolling messages, of course; start building a corpus. There may be low-hanging fruit like certain words.

Because any filtering system is imperfect, you probably want to queue these messages for human review rather than just dropping them on the floor. False positives are thus delayed in posting but aren't lost entirely, which is important in not alienating your legitimate users.

Learning

You have useful data in your existing posts: you know which ones were valuable versus not and what IPs they came from. Maybe you can leverage that.

Instead of just blocking IPs because a troll used them, you could check the history for that IP. Gee, 37 posts with a total score of +719 came in this week from there, plus three troll posts? Maybe you don't want to block that. 12 troll posts and not a single good one? That'd be safer to block. (Note: to do this, you'll need to keep track of the reasons you delete posts.)

Hobbling

If you're getting trolling from certain IPs but you also have, or might have, legitimate users there (who can't register for some reason), another approach you can take is to hobble instead of outright blocking. One way to do that (used by Stack Exchange at the user level) is to limit the number of posts that can be made in a given timeframe. Good posts (however your community defines "good") should lift the source out of the hobbling; meanwhile, at least you're cutting down on the flood. A similar approach is to hobble performance (pages just load more slowly, etc).

Scope

Applying any of these measures runs the risk of aggravating your legitimate users who happen to share IP space with the trolls. A good way to mitigate that is to only restrict anonymous users. If a registered user starts trolling, I presume you have other ways to deal with that.

Answer 2

Many forum software implementations such as vBulletin and XenForo, have a 'hobbling' or 'discouragement' feature for problematic users, which will make the users browsing session seem to fail with slow loading pages, fake error messages, etc. This function is an addon ("Miserable Users") in vBulletin, and is a stock feature in XenForo ("Discouraged Users").

vBulletin (excluding versions 4 and 5) aslso has a "Tachy Goes to Coventry" option for users, which is similar to a global ignore, whereby the member's posts cannot be seen by other other members.

Answer 3

Reddit uses a technique known as "shadow-banning", which lets users think they are posting when they're really not. Your trolls would have no idea when they are or are not banned, which is a good deterrent. They'd never know when they had to refresh their IP!

Of course, shadow-banning has become a horrifying 1984-esque totalitarian nightmare on Reddit as of late, but for anonymous users it would probably be the best solution.

Answer 4

SomethingAwful's forums require payment to post (or at least they did when I used to read their columns.) This may stop trolls or at least make it unbearably expensive to get repeatedly banned, while giving you a return for your wasted time and effort. If your community has critical mass, it could work.

You would likely wish to migrate existing users for free; rewarding them for their presence in the community with tangible assets would likely increase their loyalty and willingess to bear effort on the group's behalf.

A final point why this may work well; SomethingAwful is, at its heart, a community of talented trolls; if trolling was a job, they'd be akin to a professional organisation. The fact that this was their solution against their own trolling problems speaks for itself.