My guestbook is overrun. Help!

[jeronimo]

I'm in need of urgent help! My guestbook is overrun with porn bots and adware. Every day I have to go through and manually delete the entries added to my guestbook from these sources. Somehow my guestbook url got entered to these spiders because the same trash is being entered everday. Is there anyway to block my site from this kind of thing?
My guestbook url is: http://www.jcjunkie.com/guestbook.shtml

Thanks!

[Hoth]

Use a guestbook script that has an image prompt to prevent automated submissions.

[R4g1ng]

Rename your form names and everything to something different...or, just get another guestbook with wordban or something.