For some time now, the browser has been the most dangerous piece of software on the Web. A number of sophisticated attack crews have been using drive-by downloads and other browser attacks as an initial way to compromise a target machine. The gangs behind Gumblar, Zeus and other massive Web-based attacks have relied on browser-based exploits for much of their success. Even some of the biggest players in the industry have been taking steps to help bring attention to the problem of legitimate sites being compromised and used as attack platforms.
Source: https://threatpost.com/drive-downloads-still-running-wild-111710/74683/