In the past, I have strongly recommended the Captcha plugin by BestWebSoft, as one of my few recommended plugins, but recently I became aware of Google Captcha (reCAPTCHA), also by BestWebSoft, and find it even easier to use. This is the plugin I will use on every site I create to help reduce spam and increase security.
Instead of having to read an impossible to decipher combination of letters and numbers, or even answer a math question, all you have to do is check a box. I can’t think of anything easier. And because it has options to use this on different areas of your site like Lost Password and Comments, you can protect multiple areas of your site with one plugin.
If you’re not already using Google Captcha, I recommend you install it today.