[Ronald0]

If you are talking about random spamming bots that post random things, you need to look at enabling the verifying email for registration, then you need to add a module that stops bots. Such as captcha etc.. I am sure that will work.

If you are talking about people actually spamming you, there is no official way of banning them from the site, you can IP ban them from webhost, or you can vbulletin ban them. But they can change their IP address. Search for a cookie ban plugin that will ban the computer until the user has cleared all internet cookies.