Today I was reading a post on a message list and someone mentioned they were using a function to generate their mailto: links using HTML entities instead of the ASCII characters in order to prevent spam harvesters from snagging the e-mail address. The problem with this method, is it would be pretty easy for a harvester to re-encode the HTML entities back into the correct ASCII characters.
So, I spent a few minutes and whipped up the following code. The spamProtector() JS function takes in an array of ASCII character codes, which will be used to generate the mailto: links. I obfuscated the document.write() statement by breaking the string into chunks in order to throw off any parsers looking for certain strings.
The above function would need to be on any page were you might use the function to output an e-mail address. It could definitely be improved upon. You could add options for formatting, etc. You could even change the anchor mailto: code to it's ASCII equivalent to obscure things even more.
In order to make it easier to use the function, I also wrote a quick little CF-based function that will generate the JS-code necessary to display the mailto: link. This code will take the e-mail address you want to display and then generate the required JS code needed to produce the link. It works by converting each letter in the e-mail address to its ASCII equivalent code and then generating the required <script> tags.
Insert the below UDF into any CFML script you want to use the function in. This function should be very easy to convert to other languages (PHP, ASP, etc.)
To use the CF function to generate your spam protected mailto: link, simply use the code <cfoutput>#spamProtector("firstname.lastname@example.org")#</cfoutput>.