This was posted a while back by the Assassin's Creed UK Community Manager when similar question/ideas were put forward

As posted before - the forum admin team, are investigating methods of stopping this - however due to the way they do this, anything we do will likely impact every user, this is unavoidable - so they are being careful about it and taking their time about what they put in place.

We have several anti spam measures all ready in place and working, however since these spammers are people - they can find ways round [or simply answer the Capchas to post, which is in place for new users]

During E3 we are pulling in some more moderators, so hopefully during the times these people are available - the forums should be spam free
And most recently by Ubisoft's NCSA Community Representative

Here's the thing about Spam. It is ever changing. Not only are there bots there are real people and it exists on virtually every internet site. We do our best to delete it when it gets through and we do have systems in place. We will never detail them to you because like I said some of the spammers are real people who can read.

That being said, if you do see spam please know we will be deleting as quickly as possible so please be patient.

Thanks
Hopefully this clarifies things.

I'll go ahead and close this now.