I HATE these people!!!

I have no choice but to deactivate my guestbook in my store, because it is so badly spammed by some stupid advertisements, most of them don't even make sense to me, but a lot of them are selling Viagra and other unknown medication. I could easily receive 10 of these entries everyday and is absolutely driving me nuts! I wonder the people who spam other's guestbooks is really getting business by doing so??? Why they have to be so annoying?