In August 2007 a hacker found a way to expose the PHP source code on facebook.com. He retrieved two files and then emailed them to me, and I wrote about the issue:
http://techcrunch.com/2007/08/11/facebook-source-code-leaked/
It became a big deal:
http://www.techmeme.com/070812/p1#a070812p1
The two files are index.php (the homepage) and search.php (the search page)
