Header/Headerinclude or Footer was changed by strangers
 

Hello everyone,

My forum is 3.8.5 latest verion. Recently my forum's header or headerinclude or footer was insert an "iframe" or javascript like below:

Code:

or:
Code:

or:

Code:

or:

Code:

I had already removed any plug-ins from my forum, but I still don't know how they can change my forum's header or headerinclude or footer with the codes above

Is there anyone can help with this problem ?

Thank you.

Regards,
Calvin