There isn't a "him" in these sort of attacks. They are likely automated attacks. Just like a spam bot on twitter or automated spam texts, spam-bots can just register unlimited accounts via unlimited IP addresses and post links. I don't know enough about it to know the technology behind it, but it is completely automated. Usually a simple CAPTCHA test for account registration eliminates these things though, not sure if OS has something like that in place but they need it if they do not already.
Board loses a lot of its attraction when you've got to go three pages back to see legitimate threads from just that morning. Deleted posts need to be set to be removed from the boards, not still show as deleted.