Registrations are handled by WORDPRESS and not wpForo. wpForo just provides a "form" for ease.
Install some login/register/bot protection or security plugin. This is not a wpForo issue by any means.
I have similar issue but instead of long names, since about a month, they enter spam data in description field. Do you know if it is possible to unable description field?
Just install the plugin Anti-spam by CleanTalk and your problems should disappear immediately
Keep it in conjunction with whatever other stuff you already have including Akismet if you have it or any other as well as the Captcha - Recaptcha
It should be possible to disable the description field but try that plugin before and see how it goes
First make sure your website is protected against spam: https://wpforo.com/community/faq/how-to-stop-spam/
Then you can disable the About (description) field using this code: https://wpforo.com/community/how-to-and-troubleshooting-2/remove-about-me-section-on-members-page/#post-51146
All of them Kevin
I personally, so far, im trying CleanTalk free BUT i will not hesitate the paid versión if it was needed
I downloaded the free versión and so far I have not even had a request to upgrade to the paid version and it worked immediately with me from minute one upon installing said plugin
On my case has even stopped the registrations