Jeremy Zawodny argues that search engines should stop using links in weblog comments for PageRank in order to reduce the incentive for comment spam.
As with e-mail spam, the basic problem is that, at least for some, the benefits of posting spam exceed the costs. So, how do you attack the problem? Increase the costs or reduce the benefits.
Not counting links in weblog comments for PageRank reduces the benefits. People won't be able to use weblog comments to inflate their PageRank.
But this alone is not sufficient. There's value from a spammer just to having a link or even just a product name mentioned in a public forum. Since the costs are so low -- just like with e-mail spam -- a spammer only needs a tiny fraction of spammed people to respond to make their campaign of annoyance worthwhile.
Increasing the costs will have to be part of the solution. Spammers rely on being able to hit tens of thousands of weblogs automatically, so anything that makes this automation more difficult increases costs.
And there's many strategies out there to make weblog spam more difficult. Blacklists ban specific IP addresses from posting comments. Some require an account or a verified e-mail address before posting. Requiring entering a code from a distorted image (that is difficult for a robot to read) is another technique. Even asking a simple question (e.g. "What's the third word in this sentence?") before posting can be enough of a hassle to block spammers if everyone asks a different question.
But this will be an ongoing problem. The full costs of spam are not borne by the spammers. As long as someone, somewhere finds comment spam rewarding, the problem will exist.
[via John Battelle and Joseph Scott]