Via the Phpwiki 1.3.x UpLoad feature some hackers from russia uploaded a php3 or php4 file, install a backdoor at port 8081 and have access to your whole disc and overtake the server.
A url in the file is http://ccteam.ru/releases/c99shell
The uploaded file has a php, php3 or php4 extension and looks like a gif to the mime magic. So apache usually accepts it.
To fix this phpwiki issue at first move the lib/plugin/UpLoad.php file out of this directory.
You can fix it by adding those two lines to your list of disallowed extensions: php3 php4 Currently only "php" is disallowed.