I've been maintaining a community forum for more than a decade. We had some abusive users, so we introduced pre-moderation. Meaning, any new user is on probation for a few posts, and all anonymous posts have to be manually approved by an admin to be posted publicly. This has pretty much completely stopped the visible abuse.

However, for about 10 years, there are bots registering every day, some of them even make realistic accounts with cool and unique username, email, even description. Strangely, the email and username never match... And they make post with html links embedded. They even know to actually select the 'HTML' content type, which is an extra select input. Some bots even make a few innocent posts, before the link spam. But just too few to get past probation. Obviously, the spam posts never get approved, and accounts never get out of pre-moderation queue and yet they're still trying every day... Not intelligent enough to make more than 2 dumb posts.

Similarly, I have some work projects that have user registration with a human on-boarding process, where another person has to add the user to their group for them to share any data, none of which is ever public. So these bots are tirelessly registering, and staying in limbo forever. Thousands of useless accounts.

It boggles the mind how much energy is wasted, but I guess it must my profitable enough.