Timthumb.php is a popular script that is used to resize images dynamically in WordPress sites. This can be usually found in some popular premium themes and image related plugins. Last week, a serious security issue was found in Timthumb. Unless, you update Timthumb to its latest version at once, your site is vulnerable for hacking. This is a serious threat affecting thousands of websites and even the WordPress founder Matt blogged about this. So, please act now.