This is a short line to drop an urgent warning. We have just been hacked because of an unpatched 4images exploit. In the server logs we found attempts that lead to the hack.
So from a victim the message: UPDATE YOUR INSTALLATIONS. Probably we have been discovered by an automatic scanning script.
Maybe you are also affected already. Check if you have a file that has a name ending in .php but is a directory. I will not go into more details here.