Security breach / hijack of Universal Email template

Check the attachment... It shows a sequence where a hacker found out the code level processing in Universal Email and was able to push their own form values in a manner that populated the email.

The attachment shows the time stamps also which document #1 form found and populated via our top level form. #2 they find that they can submit their own form values. #3 a fully sent form using their own form post values.

I've never understood what these hackers gained by populating a form with spam values. I could understand gaining access to an SMTP server to push spam so this latest means of manipulating the Universal Email template page brings concern.

Anyone else see this type of activity and have a simple solution to stop unauthorized access?

I'll be adding a honeypot field to this form though not sure this will help since it seems the hacker is bypassing our public served form all together.