What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
If the submissions are blank and/or you suspect them as spam, you can set a captcha field in your form. Here's a guide that you can refer to: http://www.jotform.com/help/205-How-to-Add-a-Captcha
You can also set the limitations on your form by using a unique question or by checking the IP/browser cache: http://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form
Do let us know if that helps.