Well, there should be a filter in place that weeds out all the spamming bots. I am sure you noticed something like a series of letters and/or words that needed to be typed into a field while you were filling out the registration form a while back. That is one way to prevent the spam bots from gaining access to the site and posting spam.
There should also be a program in place to do pretty much the same thing. I am not sure of all the technical parts of it, but it should normally do a pretty good job.