One harvesting method overlooked is what I call 'screen scraping,' where spammers use commercial software to scan Web sites for e-mail addresses in their rendered or on-screen format. The simple solution I've found to render the commercial software useless is to insert spaces on both sides of the @ symbol of the e-mail address that appears on screen. Since spaces are illegal characters in e-mail addresses, the software skips right over the addresses. Now you have two layers of protection!
The third form of e-mail address harvesting from Web sites is by humans --where someone actually visits the site and copies down the e-mail addresses. I'm sure this is less common with pro-spammers, but it does exist. I have a deterrent for that as well.
First, go to our corporate Web page with your Internet Explorer browser. Highlight some names and e-mail addresses to copy and paste them. Did it work? They should have disappeared. Don't worry, you didn't screw up my Web site; just refresh and they'll come back. It freaks people out! I like getting an e-mail or phone call from a stranger that says, "Uh, I think I just deleted stuff off your Web site." Of course my response is, "Why are you trying to bulk copy e-mail addresses from my Web site?"
The trick isn't really protection, it's more of a deterrent based on the user's skill level. It only works with Internet Explorer browsers. Just add onMouseUp="document.selection.clear()" to the <body> tag of the Web page.
If you use Edit Menu -> Select All -> Edit -> Copy, you can save that clipboard data to a plain text file and work from it.
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This was first published in July 2004