As the web continues to play an ever increasing role in information exchange, so too is it becoming the prevailing platform for infecting vulnerable hosts. In this paper, we provide a detailed study of the pervasiveness of so-called drive-by downloads on the Internet. Driveby downloads are caused by URLs that attempt to exploit their visitors and cause malware to be installed and run automatically. Over a period of 10 months we processed billions of URLs, and our results shows that a non-trivial amount, of over 3 million malicious URLs, initiate driveby downloads. An even more troubling finding is that