There are daily spam forum posts from bots, and it'll be 'whack-a-mole' until there is a better registration system.
Don't click on any links in posts unless it looks like a bonafide post about chess from a regular member as tempting as the description of the link may be. Even then be wary. Some of the links may well try to install malware on your system.
They'll post in the main channel at least as they won't be pro members.
Another solution (with a moderator) would be only release main channel posts to the forum when they have been vetted. This would be a little slower for non-pro members, but as most of the posters are pro and the only benefits of non-pro outside of special unlock days are seeing the free courses, as long as they do get approved is unlikely to be much of a problem. Most main channel posts from non-pro members would be about the site and membership so a moderator might be a good person for an initial answer anyway.