Attackers increasingly are engaging in IP cloaking to infect Web visitors, where they bypass malware detection systems by serving them clean pages while they drop malware on visitors to the site, according to a new report by Google's security team.

"Over the years, we have seen more malicious sites engaging in IP cloaking. To bypass the cloaking defense, we run our scanners in different ways to mimic regular user traffic," said Lucas Ballard and Niels Provos of the Google Security Team, in a blog post yesterday.

Google's research is based on more than four years of data gathered from its Safe Browsing API service. Google's Safe Browsing API is an online database that contains known malware-rigged Web pages and phishing sites. Chrome, as well as Mozilla's Firefox and Apple's Safari browsers, use the database, as well.

The search engine giant's analysis of the malware-evasion methods used by the bad guys is based on 160 million Web pages hosted on some 8 million sites.

As of summer 2010, 160,000 or so websites were employing cloaking domains, according to Google's report, which covers five years of data. This technique peaked two years ago, when there were some 200,000 websites with IP cloaking, up from more than 50,000 earlier that year. "That peak coincides with a large-scale attack, where thousands of sites were infected to redirect to gumblar.cn, which actively cloaked our scanners," Google says in its report. "Although the increase in the graph is partly due to improved detection of cloaking domains in our system, we believe that it is representative of the general state of cloaking."

Attackers are also using social engineering and drive-by downloads, according to Google. Socially engineered Web attacks try to lure a user into following a link or downloading software.

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