The warning comes from Lorelle on WordPress after it was discovered that a nasty attack is exploiting security holes in previous versions of the blogging software, creating a new “hidden” Administrator account and getting right down to the database level. These attacks are said to be “growing by the hour”. Lorelle writes:
There are two clues that your WordPress site has been attacked.
There are strange additions to the pretty permalinks, such as example.com/category/post-title/%&(%7B$%7Beval(base64_decode($_SERVER%5BHTTP_REFERER%5D))%7D%7D|.+)&%/. The keywords are “eval” and “base64_decode.”
The second clue is that a “back door” was created by a “hidden” Administrator. Check your site users for “Administrator (2)” or a name you do not recognize. You will probably be unable to access that account.