I've recently created a ticket in LW issue tracker, that suggests two possible solutions:
I prefer the second option. The ticket was accepted, but with no information on which variant will be implemented.
If the attacker is willing to put work into spamming this specific site, which is possible, then neither of these gets us anywhere, since you don't need karma to give karma. To be an effective barrier, you would also need to limit voting to those with positive karma. I'd support that.
EDIT: Admins would then have to track down and delete those accounts which gave positive karma to spammers.
I think the second option is preferable. Is anyone currently working on this? If not, I'm going to try to implement the change myself, seeing as I suggested something like this months ago to no avail.
A captcha is now presented when submitting an article with less than 1 karma.
Will see, but I expect this won't be air-tight, since the spammers manage to register anyway, and there is already a captcha on registration. There are tools for solving captchas cheaply, but not for posting good comments.
"X can't be that difficult to implement": something one probably shouldn't say about an open source project unless one is about to give it a go themselves.
By writing that captcha was implemented because it was easy to implement, you suggest that easy-to-implement property has nontrivial explanatory power. I disagree, since I believe this property also holds for other alternatives, so can't explain the choice, and shouldn't be used as an argument. It's just a matter of rationalist nitpicking.
(It's more difficult for me, because I don't know the project (or python, for that matter), but must be trivial for people who do. In any case, the intended meaning, as applied to Karma limit, is the same as with captcha in the sentence that originated the exchange, so it refers to how difficult it would be to implement the Karma limit (instead) for the person who implemented captcha.)
I hate to say it, but if you grant posting privileges to anyone that's ever received a single upvote, you've just given an easy-to-use and powerfully obnoxious weapon to anyone who feels like trolling the site. From what I remember, the offending accounts aren't removed anywhere near as quickly as the threads they spawn are.
Spam (curiously enough, always for jewelry) accounts for maybe two-thirds of what comes through the LW Discussion area's RSS feed these days. So although the moderators have been doing a great job of quickly removing it from the site itself, it remains a substantial annoyance for those of us who keep track of LW through a feed.
I think it's time to revisit the possibility of making it harder for people to post in the discussion area. Clearly it would suffice to limit posting privileges to those who have a positive karma balance. If that seems too draconian, as it did to some people in the previous thread, it would probably be enough to limit posting privileges to those who have ever received a single upvote on any comment they have ever posted.
Would any administrator care to undertake this? If so, many thanks.
(My apologies if an unfinished version of this post briefly appeared on the site some hours ago.)