Any more news on this? I'm getting spam sign ups too. Currently at a rate I can delete them but adding reCAPTCHA would solve the issue immensely. If anyone can recommend a suitable plugin in the mean time I'd appreciate it.

You should try them and find the best for you. There isn't any recommendation here. I can only say that most of those complatible with wpForo registration page if the "Email confirmation" is enabled.

Okay, will try some. Looking for a free one. Will report back my findings.

Okay, so seem to have found a good plugin for this issue on my second try at a plugin. WP-SpamShield. Since installing I've had no spam registrations and other new users have registered fine. Sweet.

Thank you for sharing this plugin name.