Google has long been wise to ways of comment spammers, but that doesn’t stop many comment threads degenerating into spammy lists of “work from home” comments and link spam. Akismet and similar spam filters catch most of it, but judging by the sites I see every day, these filters let plenty of spam through.
Although many publishers have removed comments from their sites, largely because they don’t want to deal with spammers and other “problem commenters,” hundreds of thousands of bloggers allow their users to contribute to the conversation.
If you think having comments on your blog is valuable, you have to deal with the spam. I’ve found that one of the best ways to reduce spam is to close comment threads after a while. This works because the majority of comments are posted immediately after an article is published. Publishers only have to moderate comments for a short time, and spammers have less of a window to get their comments into the thread.
For a moderately popular post, there’s a clear pattern to comment posting. The peak is almost immediate: usually in the first one or two days after the post is published. If the article continues to attract attention, the plateau may continue for a few days, but it’ll eventually decline, and after a couple of weeks, comments are sporadic. The most valuable interactions usually happen right after publication.
Closing comments after a couple of week will reduce the total number of comments and limit conversations — some potentially great comments won’t be published — but publishers should balance the risk of restricting comments with the benefits.
A moderately active blog that’s more than a couple of years old may have hundreds or thousands of posts; some have tens of thousands of posts. Monitoring every one of those posts for spam comments is a full-time job, sometimes it’s several full-time jobs. Those resources are better invested elsewhere. Allowing comments for a limited period drastically reduces the number of posts that publishers must actively moderate.
In fact, what tends to happen is that older posts aren’t actively monitored. Comment spammers love this type of blog. They can slip spam onto the site in the confidence that no one will see it. For some types of spam — link spam in particular — spammers don’t care whether anyone sees it. What matters is the link from a popular site. This sort of spamming isn’t hugely effective — smart bloggers no-follow links in comments anyway, but that doesn’t stop spammers and their bots.
Closing comments on older posts does little to limit the contribution that readers can make to site’s community, while massively reducing the amount of spam that site owners have to deal with.
Many comment systems recognize the benefits of closing comments after a predetermined period. Disqus has a setting that allows publishers to choose a number of days before the thread is closed. WordPress’s built-in comments have a similar option; you can find the option under “Setting -> Discussion” in the WordPress admin dashboard.