After following the advice in a previous question (here) I've managed to nuke my spam comments. I now, however, find that every day I have a few new members sign up to the site with rubbish e-mail addresses like firstname.lastname@example.org. I could close sign-ups but I'd rather not as I'm hoping the site will beceome a bit more popular and would like to encourage comments.
I have been using Recaptcha which has the added benefit of helping to translate literature. (!)The plugin linked above will add Re-Captcha to your comments or registration form or both. It also has features like themes for the captcha forms. Definitely worth looking into.
The easiest way would be to include a Captcha on your registration page. Most Captcha systems depend on the user's ability to read a word or answer a question (i.e. "What is 2+3?"). Automated systems like these spam bots have trouble with Captchas, but they're by no means perfect.
However, I discovered today a Captcha plug-in that protects the registration page that requires the use to drag color-coded elements onto specific portions of the screen: KeyCAPTCHA.
This might help. But any spam bot deterrent is better than none.
I would recommend Block Spam By Math Reloaded for the following reasons.
- There is no registration to a third party site (which always worries me because if they pull the service you could be left with broken forms).
- It has a decent score on the Wordpress site, I find the community scores to be generally quite good at highlighting good/bad plugins.
- Superfast to install and set up.
- Can be used to stop comment/login/signup/form spam
- It has been updated this month (July 2011) so it at the moment at least in current development