Comment spam is the bane of most blog owners. It's everywhere and if left untreated will turn off reader in a heartbeat. It's controllable and manageable, and removing it can some times be a daily ritual. But there are solutions to make controlling comment spam pretty easy.
If you host your own blog there are several plug-ins that help fight spam. On of my favorites is Akismet. It's very easy to setup and works pretty good. The basic use is Akismet check certain keyword, IP addresses and URL's in its database and marks the comment as spam. The administrator has the ability to review the marked comments and decide if its really spam or whether it was a mistake.
Another form of spam comment control is using a plug-in called Captcha. Basically, the user is required to enter a random set of characters in a text box before the blogging software will save the comment. This is a big deterrent for automated comment spammers since your blog wont even allow the comment into your blog until the Captcha is passed.
Most software can require a commenter to be a registered user, or comments are accepted but are put into a queue for the administrator to manually approve. If you have a low volume of comments this can be an easy solution. If you have a lot of comments an automated solution is about the only path to take.
When it comes to requiring visitors to register just to leave a comment, a lot of visitors will just move on to another blog. Blogs are designed to encourage feedback and participation. Requiring someone to fill out a form doesn't seem very inviting. Implementing these techniques will allow your readers to comment, which is what you want, right?
How do you handle comment spam on your blog? Is it a big problem for you?
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