Google just released a study entitled The Ghost in the Browser: Analysis of web-based malware [pdf document] in which it claims that 10% of websites contain malicious malware. It conducted an “in-depth research on 4.5 million Web sites and found that about one in 10 Web pages could successfully “drive-by download” a Trojan horse virus onto a visitor’s computer. Such malicious software potentially enables hackers to access sensitive data stored on the computer or its network, or to install rogue applications.” [cnet news]
Not only that, but according to another article on cnet,
An average of 8,000 new URLs containing malicious software emerged each week during April, Cluley said, adding that the notion that such software resides only in the darker corners of the Internet is very outdated. Seventy percent of Web pages hosting rogue software are found on legitimate sites targeted by hackers, according to Sophos.