Previously, you would be presented with security questions when making your first post, or when sending a PM if you had less than 5 posts.
I've changed this so you will no longer be asked them when sending PMs so long as you have at least one post, as it doesn't seem spambots are even able to register (based on looking at Guests in the Who's Online), and if either of the two new registrations that I don't recognize are spambots, they haven't been able to post.