Thread:Project:Support desk/Hidden texts automatically inserted in old and new pages/reply

Which version of MediaWiki are you using and which MediaWiki version(s) have you been using since November 2014?

Before you start cleaning up the mess, you must find out, how the attacker gained access to your server. Did he have your FTP data? Did he log in somehow (to Plesk or what you are running)? Did he maybe gain access through a completely different installation in your account (e.g. you still have another system running,for example an old WordPress version or Joomla or so)? Or did he maybe infect a completely different account and could then infect your files?

Check back with your host to figure that out!