Hi @hihored,
wpForo has a built-in reCAPTCHA. Have you enabled it?
Please note that all WordPress websites are under hard spam attack. wpForo doesn’t have any relation to your spam issue. You installed a forum plugin and opened the user registration so you should be able to protect it. We have a large instruction for you: https://wpforo.com/community/faq/how-to-stop-spam/
Spam is everywhere! It doesn’t matter you use wpForo or not. If you enabled user registration then wait for spams… wpForo doesn’t handle user registration and doesn’t have any affection on number of spam registrations. All processes of user registration are still performed by your WordPress core functions. So you should find solutions to protect WordPress not wpForo.