Jani Hartikainen has posted a reminder for all developers to filter their incoming data. He points out a specific issue with arrays.

You've written a PHP based web app, and you've made sure it doesn't cause errors if the user submits unexpected values via any URLs or forms. But there's something you quite likely forgot to test: What if the data that's expected to be a singular value happens to be an array? If you assumed a GET or POST parameter will never be an array, your site probably joined the ranks of several high-profile sites that go into funny-mode when given unexpected arrays...

He gives an example exploit of how PHP handles arrays, both in normal PHP and in the Zend Framework, and how those could be interpreted and data could be injected into your script.