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The fact that malicious URLs that initiate drive-by downloads are spread far and wide raises concerns regarding the safety of browsing the Web. However, to date, little is known about the specifics of this increasingly common malware distribution technique. In this work, we attempt to fill in the gaps about this growing phenomenon by providing a comprehensive look at the problem from several perspectives. Our study uses a large scale data collection infrastructure that continuously detects and monitors the behavior of websites that perpetrate drive-by downloads. Our in-depth analysis of over $ 66$ million URLs (spanning a $ 10$ month period) reveals that the scope of the problem is significant. For instance, we find that $ 1.3\%$ of the incoming search queries to Google's search engine return at least one link to a malicious site.

Moreover, our analysis reveals several forms of relations between some distribution sites and networks. A more troubling concern is the extent to which users may be lured into the malware distribution networks by content served through online Ads. For the most part, the syndication relations that implicitly exist in advertising networks are being abused to deliver malware through Ads. Lastly, we show that merely avoiding the dark corners of the Internet does not limit exposure to malware. Unfortunately, we also find that even state-of-the-art anti-virus engines are lacking in their ability to protect against drive-by downloads. While this is to be expected, it does call for more elaborate defense mechanisms to curtail this rapidly increasing threat.

Niels Provos 2008-05-13