Some times ago i've added a Forum in my WP website with phpbb. I didn't have captcha on registration so soon my forum was filled with spam users and spam posts, obiuously all made by a bot.
The spam leves was so high that my hosting ghosted my site because they said that Google was going to put in blacklist my ip.
I want to say that my site was totally legit and white hat, my niche was technology, a simple tech-related blog.
I've deleted the forum and the links from my site…