Hacked site and problem with login cookies

Hi,
two weeks ago I’ve submited a post about my problem to login.
And one week ago some posts appeared in my site, olds and news. None of then was done by us. I don’t know what is happening. Can some one say what is happening and what I can do, please?
If just the owner (main admin) can do something about this, could someone say me that, please? I don’t what involve him, but if it’s the only way, I prefer do that then let my site stay the way that it is now.
Thank you