If you are using the php accelerator with your UBB please read the security notice at http://www.php.net
( top of page ).
If you are a system administrator you will want to patch or update your php install as soon as possible.
If you are not a system administrator but are hosted you'll want to check with your hosting company and ask them if they are aware of this very important security notice.
It is most important to note the following line from the bulletin
Honor The Victims
Please notice, that you are not only vulnerable if you run scripts that use uploaded files. You are vulnerable if you run any script!