I can't imagine how it can be related, or whether it is related, but since the forums search is reenabled for guests (the last two days), the amount of new registered (known) spammers increased significantly to 25 to 40 per day.
Luckily they are recognized by our anti-spam system and never approved, so they can not post.
To see if it is really related or not, I disable Forum search for guests again (hopefully temporary).