About a month ago I posted about tweaking timthumb to work with CDN. Timthumb is a great script, but great scripts also have bugs. A recently discovered one is a rather serious bug. It can allow attackers to inject arbitrary php code onto your site, and from there onwards, pretty much take control over it.
Luckily no websites I know or maintain were affected, possibly since the htaccess change I used shouldn’t allow using remote URLs in the first place (and also it renamed timthumb.php from the url string, making it slightly obfuscated). I still very strongly advise anybody using timthumb to upgrade to the latest version to avoid risks.