Web Form Spam

[Mark Greenfield]

Recently we have begun to experience an increase in spam generated from some of our web (HTML) forms. How do you deal with this? I'm concerned that some solutions may be inaccessible (I.e. CAPTCHA).

[Michael Fienen]

Try this out: http://www.modernblue.com/web-design-blog/fighting-spam-with-css/

The trick is to add something to the filling out of the form that requires human level cognition, or give the bot a field that it will fill in that a human can't see.

[Kyle James]

I remember reading a few weeks ago that there is some body that says they can beat Yahoo's CAPTCHA...

Also there was the report about the Stripper software that was a creative way to beat CAPTCHA...

Personally we just delete the messages. It hasn't really gotten out of control, though. Maybe I'll get one a week.

[Chris Pollock]

I use a double pronged approach on some of my forms.

I have a field that must remain blank (or else it returns a message saying that we suspect you may be a machine). You have to be careful what you name those remain blank fields for a couple of reasons: 1) Google Toolbar autofill - it might stick a value in there unbeknownst to you and 2) It has to make sense to someone who might be seeing the field with a screen reader (maybe that's not an issue if you set the visibility off).

Secondarily I put a hidden field in my form that is populated when the onclick event fires on the submit button. I then check for that form value on the server side to make sure it's populated with the correct value. This should prevent bots from posting to my page. It basically requires the human interaction of clicking on the button to pass validation.

I'm not sure what the second option does to accessibility. I do not know how screen readers handle onclick events in JavaScript. I guess my assumption is that when you click enter on a button it fires that event so it should work just fine. Its also right in line with the kind of client-side validation that most people have on their forms anyways (like checking that required fields are filled in).

If you're interested in some code let me know.. I was going to blog about this, but have not gotten around to it.

[Anthony]

Wouldn't the alternative of checking the referring script on the post page be better than your second technique since it doesn't rely on Javascript? Is there some reason why you wouldn't do it that way?

[Chris Pollock]

Checking the referrer is probably a better way. I wasn't really familiar with that approach until I started reading this thread. Thanks for suggesting it.

[Anthony]

Oh, cool. Glad I said something.

[Genevieve Howard]

This article was helpful for me
http://www.digital-web.com/articles/bulletproof_contact_form_with_php/

[Nathan Sgroi]

If you are using asp.net at all, you could try the NoBot control that comes with their free ajax extender control toolkit. Here is a link to a demo: http://www.asp.net/AJAX/AjaxControlToolkit/Samples/NoBot/NoBot.aspx

If you are not using asp.net or some form of server side code, I'm not sure how you would stop spamming.

[Kevin deLeon]

I have been using reCAPTCHA (http://recaptcha.net/) on some of our forms with success. I am sure it will only be a period of time before this is useless as well. It has an audio CAPTCHA built in for accessibility, and is fairly easy to implement.

[Anthony]

Seconded. I have had great results on our blogs with reCAPTCHA. The only spam comments that have come through are obviously human. Before that they were getting hit so much I have to have registration on, which meant no one went through the effort required to comment.

[Stephanie Leary]

I'm in the minority, but I refuse to put the onus on the user in any way. Instead, I do all the spam prevention on the backend. I use Akismet whenever possible, like this form.

[Mike Adams]

The forms we were having problems with did not ask for any urls. So, I wrote a script that checks each item in the object. If any of them contain "http://" then the script stops and returns to the form page.

We haven't had any spam on those forms since.