look at that spam in the General section. how about making this forum private, which means anyone can request to join, anyone can see or read the contents, but must be approved by the moderator if they want to make a post (one-time approval).
on how that can be done, maybe a new section called Verification should be made, it's the only section where new unapproved members can verify themselves by making a post there. even if there are spam bots making spam posts, it won't be much a problem because they can only post there, not any other section. here are the steps :
1. a person sign up for an account (unapproved/unverified by mod) - he can browse and read any posts, but cannot post. so all upcoming new members will be automatically in the blacklist "for posting".
2. he wants to post something, but first he have to make a verification post in the Verification section with a post like "Hi, my name is, i bought the game blablabla, i'd like to make a post regarding some of in-game things that i don't understand blablabla" something like that.
3. then the moderator approve his account by removing him from the blacklist if the mod deem this guy a human, and send them a direct message saying "hi, thank you for joining us, you may make a post from now on" something like that (can be automated).
i know it doesn't guarantee that this new guy won't post spams later, but at least this way might reduce their numbers.
well, it's just a suggestion.