I found out a great trick to tackle this from someone else with the same problem and who was using the same webspace. Just change the name of the folder for the guestbook (and the accompanying links) and that would fox the spammers (until two months later they had found you again).
But then I found I could no longer change the folder name on my webspace, nor could I upload a new configuration for the guest book. By this time I was getting ten to twenty entries a day on the guest book. Most of these were for viagra (how did they know of my impotence?) but there were others which I think were related to sex (but in other ways – see below).
Some of the guestbook spam pointed to pages on sites run by educational institutions in the United States. I followed one of these up and pointed out to the owner of the sub-site that this was what was happening. I received a very courteous e-mail in reply which thanked me and promised that the site would be taken down. But it was a just a mere drop in the ocean – and still more came.
I did laugh at a few of these spam entries. Like the example shown above - my boss compels me to post these links on your site. Unfortunately, most of the spam entries didn’t even have cheeky humour to redeem them.
Anyway, it finally got to me, and I secured a new guest book with a spam filter from Smart Guestbook, and saved off the 40 or so legitimate entries from my old guestbook to preserve in aspic and lovingly reproduce on my site. I’ll let you know if the new spam filter works.
