@ WPyogi thanx for the great help…
For all others, this code is added by plugin Facebook / quiknotes, the directory name of the plugin is quiknotes. The plugin is not available anymore on ww.wp.xz.cn.
So delete/deactivate the plugin and check your system as WPyogi mentioned before.
Did somebody checked that issue?
Looks like malware, but no entry in mysql or php files. Any idea ?
Regards
David