I’ve been using this plugin for a few years now, and I must say, it’s the very best anti-spam plugin on the market. It’s not free, but it’s not expensive either. The plugin is called Cleantalk. You are going to want to go HERE to get Cleantalk, or check it out. The spam blocker works on all sign-in pages, forms, and everything that takes input…and it’s got a firewall, so it blocks both IP addresses and email addresses…it’s very effective. I have never liked Akismet, and those captcha things are a pain in the butt in my opinion, so I don’t trouble my viewers with captchas when they register. I don’t need to. Check it out!