Spammers are using a contact form on our Wordpress site to spam us, but I can't find which form it is. It's (presumably) from our site because it has the standard footer "This e-mail was sent from a contact form on OURSITENAME (http://www.OURSITENAME.com)". The subject was just 'Contact Form Submission' so I changed the subject line on our main contact form to something different and the spam's still coming through with the original subject line. So I know it's a different form, but to my knowledge it's the only one we've got which sends an email to us in this manner.
Under Dashboard > Contact, I have four forms. Our normal one, and two others which have different subject lines. So it must be somewhere else. I checked the message source and there's nothing in there to indicate where it came from.
Does anyone know how to track this down?