Someone has hacked into my site and is completing the text boxes used for requesting a price list and brochure with reams of spam, some of which is disgusting, complete with HTML addresses advertising various web sites.

Whilst I am able to delete these requests when I receive them, is there anyway I can stop this guy/woman from piggy backing my site please.

I have tried to find a way of limiting the number of characters in each text box i.e max characters, but I cannot find a way of doing so.

Any advice would be most welcomed.