This page generates a bunch of bogus email addresses, and links back to itself. The theory is that these scanners will get caught in a loop. There is a tag in the header that tells Google to not follow these dummy links. If you know how to stop other legitimate trawl bots from getting caught here too, please let me know (see email off root page).
This idea is copied from http://xpenguin.com/blackhole.php.
Here's the bogus email addresses (the first one is real for testing the success of this page from time to time):
And here's the links back to this page:
Written by Andrew Chapman - April 2003
Here's a link to the PHP (if you're not using PHP for your web scripting you're just plain stupid) source for this page: blk_hle.src.