What are spam crawlers?

Spam crawlers are automatically programmed bots that steal your email address from the web by various mechanisms and use it in bulk email or other purposes usually referred as spam. This process is also known as email address harvesting.

Contact details, terms and policies, about pages and pretty much everywhere on your site where you publicly expose your email address, is a great resource for crawlers.

The crawler or so called harvester automatically searches the HTML content of your web site, usually scanning the link tag

<a></a>

So what’s the idea?

There’re few workarounds for protecting email addresses and you’ve probably seen solutions like displaying the email in format: info (at) invoicebus (dot) com, embedding the email into an image, implementing contact form etc. However, in all cases you don’t get clickable email link, so here we’re going to use a little hack.

Beside the href=”mailto:” attribute, the spam crawler scans every HTML code that contains “@” sign, so can easily figure out and extract the actual email address. Our objective is to keep the crawler task difficult as much as possible.

In fact, we’ll programmatically hide the email address behind variable and dynamically print it in run-time, exactly when the page is rendered by the browser. The crawler won’t be able to find it anywhere in the code.

If we divide the email address on 3 parts,

we can assign the value sequentially in two steps by concatenating strings.
Here’s the JavaScript snippet for it:

<script type="text/javascript">

     var emailE = 'invoicebus.com';
     emailE = ('support' + '@' + emailE);
     document.write('<a href="mailto:' + emailE + '">' + emailE + '</a>');

</script>

The code will display the following link in the browser:

You can even write your own JS function that transforms the letters with custom pattern, but for now I’ll stick to the basics.

Of course, you also have another option of not using the JavaScript by directly encoding the value of the HREF attribute with HTML ASCII encoding or URL encoding.

<a href="mailto:yourname@domain.com">yourname@domain.com</a>

<a href="&#109;&#97;&#105;&#108;&#116;&#111;&#58;&#121;&#111;&#117;&#114;&#110;&#97;&#109;&#101;&#64;&#100;&#111;&#109;&#97;&#105;&#110;&#46;&#99;&#111;&#109;">&#121;&#111;&#117;&#114;&#110;&#97;&#109;&#101;&#64;&#100;&#111;&#109;&#97;&#105;&#110;&#46;&#99;&#111;&#109;</a>

In both cases, the browser will display the following:

yourname@domain.com

I quickly wrote a simple HTML ASCII encoder that can be used to encode your email addresses or any text you want.

There’re couples of other methods available, but I believe these two are the most effective ones, so far. It’s up to you which one you’ll choose. For us, JS method works pretty well.

A little effort and a few lines of code on your site will save you from tons of unsolicited and junk email later.


Now let me hear your thoughts on it.
Have any suggestions of how to improve these methods, or maybe some others we haven't heard about?

Author information

Stefan Chachovski

Co-founder of Invoicebus. Huge lover of nature, science, and chocolate cherry cordials. He occasionally writes on this blog about Invoicebus' stuff. Hello him on Twitter or subscribe to his updates on Facebook.

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