spam on community website

we have a local football club which has a guestbook. we are having serious problems with people putting messages on the guestbook trying to sell stuff - viagra etc. the real problem is the amount of adds. there are now over 1,000 adds. we have tried taking the guestbook off line but you can still access it by googling it and the adds are only increasing. can anyone help?

If you have taken the guestbook offline then what does it matter? And why not remove it altogether? Does it actually serve any useful purpose? Most guestbooks don't. Alternatively make it available to registered users only.

What software are you using for this?
If you can put the comments in "moderation" first you can at least stop them being viewable by the public.
If the site is running on a linux server there are a number of tools available to help block spammers, as a lot of them are completely automated.