Inputing -1 in form submission

Hi All,

I appear to have someone who is submitting forms on our website and keeps including "-1" in various fields. They're even appearing in hidden fields passed on in the form.

Some examples:

You have received feedback for image: _sep_2008_ 128.jpg in category crops - -1'

Did I find it useful?: yes,no
Im a: teacher,student,pupil,other

Comment:

You have received feedback for image: -1' in category crops - oilseeds

Did I find it useful?: yes,no
Im a: teacher,student,pupil,other

Comment:

You have received feedback for image: _sep_2008_ 128.jpg in category -1' - oilseeds

Did I find it useful?: yes,no
Im a: teacher,student,pupil,other

Comment:

The time between the form submissions and the data returned does look like some kind of automated submission.

Is anyone aware of an "attack" like this on a ColdFusion server?

Best wishes

Trevor