Google redirects to porn malware site

A message promising Paris Hilton topless includes a hyperlink that appears innocent - the words “download it now” link to a page that begins http://www.google.com/pagead/iclk?sa=l&ai=trailhead&num=69803&adurl=http://…
[this link won't work since I've truncated it on purpose].

The site automatically downloads a Trojan malware called “trailer.exe”. Nothing new under the sun….