On the PHPClasses.org blog today there's a new post looking at the security vulnerability that effected not only PHP but lots of other languages making them susceptible to attack from the outside.
In PHP and several other languages used to implement Web applications, arrays are used to store the values of request variables such as $_GET, $_POST, $COOKIE, etc.. IF you receive a request with a large number of request values, until recent versions PHP may run into trouble.
He goes on to explain why there's an issue with the array overloading and what PHP has done in recent releases to help correct the issue - the max_input_vars setting in the php.ini. He also points out that this is not a new issue - it was originally identified back in 2003 (with a video of the original presentation). He points out that the most recent releases of the PHP language have this fix in them and, if at all possible, you should upgrade to protect your applications.