This had happened with almost every forum i've ever helped run. The bots are extremely annoying. Just report their posts and that will send an email to the moderators immediately so they can delete it. As for a solution, i have yet to find one sadly. Maybe forcing new members to only be able to create their first thread/post in new member intro section and from there they unlock posting/threading privileges everywhere else
Linking the forum software to stopforumspam helps as well as 1 other service.
Another forum I'm on is spammed incessantly by third world particleboard UK kitchen shilling pricks. The head prick hired a SEO in Indonesia or something and has actual little pricks who only take a day off to bow and grovel toward Mecca and the rest of the time they are posting about their particleboard kitchens.