The Zend Developer Zone has posted security tip #15 today, focusing on an easily forgotten aspect of web development (not just in PHP) - forgetting to remove temporary files.
As developers, most of us are very messy. I've worked on countless projects and at each either run across or left a trail of diagnostic files laying around. (info.php, test.php, doMe.php, etc.) These tiles, if found by someone with nefarious intent, can leak valuable information about your system.
Always remember to remove these types of files...as Cal puts it:
It would be a shame to spend all that time securing your application only to leave info.php or worse yet, a "quick piece of code" in test.php that could potentially leak dangerous information about your system. Don't help the ad guys any more than you have to.