My blog is hacked by someone.
Someone inserted a long advertisement as below just after the
<div style="position:absolute;left:-48667px;top:-65558px"><!--779212266--><h1>sony ericsson k300i downloads</h1> Nokia <a href="http://www.jjsdesign.net/forum/?info-about=632" title="sony k300i downloads ericsson">sony k300i downloads ericsson</a> ........ in our database that you can offer on your site! </div>
This kind of advertisement appeares in the index page and archive pages, doesn't appear in the 404 error page.
I have upgraded WordPress to 2.7.1 and turned off all plug-ins, and using the default theme, however it appears.
Is there anyone know how to fix it, or the similar case?