Sadly, this happens to far to many good people.
There are no free or easy ways to clean up a hacked website.
Unlike your computer, a website does not have viruses which can be removed. A website is just a collection of files.
In this case hacker appears to have modified files (hacked by…). Which files were changed or need to be “fixed” is not possible to know without opening “the hood.”
That said, you’ll need to have someone work to assist you in replacing all WordPress core files, along with locating and removing any back door scripts that may be hiding within your code or files.
You may find this link helpful:
http://codex.wordpress.org/FAQ_My_site_was_hacked
