A quick and dirty trick is to add a text field (not a hidden field) named subject to your form. Hide this field from your users using CSS (input[name="subject"] { display: none; }). Most spam bots will fill that field. If that field is set, assume the form was submitted by a bot.

This trick can be used in conjunction with other methods for defense in depth.

In reply to Re: newb: Best way to protect CGI from non-form invocation? by ikegami
in thread newb: Best way to protect CGI from non-form invocation? by JCHallgren

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