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Hate to break it to you Chase, but we already have a captcha on user creation. In fact, we have *TWO* captchas (reCaptcha, plus a simple math question presented as an image) required for user creation, and the bots involved in these user creations seem to crack crack both. I tend to wonder if they're using a "mechanical turk" type of system to outsource bulk captcha breaking to humans.

Only reason they very rarely succeed at actually posting content these days, is because of a custom Mediawiki extension I added, which blocks any edits which add new external URL links if the user account was created within X hours of the attempt. (Note, it does not block external URLs that are not formatted as Mediawiki links, such as the participants page of course)

Perhaps I should augment this extension to remove users whose only attempted edits during a 1 week period were blocked in this fashion?

My experience with captcha locked registration, is that at some point someone, most likely a human, provides an answer to at least one question. After this bots will register like crazy. On my site I had non googlable question, which holds bots for a month or two, but sooner or letter they will come.

The only way to deal with it, is to remove old questions and generate new ones.

"Perhaps I should augment this extension to remove users whose only attempted edits during a 1 week period were blocked in this fashion?"

That policy sounds pretty reasonable, as long as it is clearly written somewhere new users would see.

Make it 3 days and that'll do it for me. We should also nuke users without any posts that registered more then 3 days ago as well (and were not added by an admin), or something.

I think there are some features enabled for registered users. Something with cookies but I cannot recall what are they. So, quiet registered users have a right to exist.

But quite folks do not contribute, so it is probably fine to sweep them away as the bot candidates.

There are not a major amount of benefits to being registered aside from posting. I think it keeps your layout and settings and such. But most active people (even readers) have at least one edit under their belt. Since this is about robocode, you usually make a robot and enter it into the rumble.

Actually, now that I think about it. I think Voidious used Asirra to prevent issues on the berrybots wiki. Now asirra is closing down this year, so we can't use that. But there should be some other image based captcha's around.

As we all know, classification is a very difficult AI problem, but is almost trivial for us humans. :)

Usually, it is sufficient to ask what is "2+2", may be in the form "two plus two" so it is not that obvious for a parser. Since, we are fighting attacks not designed against this particular wiki, it will be sufficient. Once, a traitor give the answer to this question to a bot net, we will ask what is 2+3, and so on.

We could just randomize it so it's 17 + 21, and then just tweak the way it is said so it becomes thing likes "one before eighteen plus one past twenty"

Wow, I would not pass such captcha on a first try :). It sounds like the french way to call numbers, which I believe, is not very common.

Oh, hrm, fair point. French numbers are way more difficult then this though. This is just offset them by 1 each.

I decided to try the registration process. We do have a math question and a number image recognition images. But these bots are advanced. They clearly can parse/recognize numbers and do simple math with them.

I think we need at least one captcha which deals with something but numbers and we need it asap. My rss feed is spammed by new registration announcements way more often than I wish to know.

Or, as Rednaxela noted above, they could just be outsourcing it to humans. Though if they are advanced bots, we could try something like Asirra, which makes users select only photos which have a certain type of animal in them, though it seems Asirra itself won't be around for much longer. (Voidious, since you use Asirra for the BerryBots wiki, you may also want to look into a new captcha system.)

We might want to consider locking registration until we can come up with a solution. The wiki isn't particularly active at the moment and there has been 166 registrations since they started on September 23 (and 1 which is questionable). None of them have posted a single thing. That averages about to around 10-11 new users a day.

I guess that would be fine for a few days, but if someone's willing to go to that trouble, why not just implement one of the solutions that have already been proposed, such as deleting accounts that only post with external links in their first few days, or your suggestion to have a hidden textbox that must be left blank?

That's true. I would do it, but I don't have shell access. So we have to wait for one of the senior admins.