Unintentionally unsubscribing

[René_Kamine]

Hi

I have a checkbox in a form to subsribe to our marketing. In the marketing optin field there are either Yes or No values. If that field on the form is left empty a No value is either replacing the Yes (they are already opted in) or auto populating a No value. The latter is OK, but if that check box is left blank I don't want the Yes (they are opted in) to be overwritten with the No value. How do I get around this?

Form can be found here - http://pages.supercars.com/gc-sms-non-mktg-optin.html

Thanks in advance.