A recent study by Sunnyvale-based network security firm Blue Coat Systems has revealed that about 40 percent of all malware infections use search engines as their entry point.

The security firm, which released its 2011 Mid-Year Web Security Report, examined Web-based malware ecosystems, including the 10 largest malware delivery networks. The report also examined the interactions of malware ecosystems, including user behavior, malware hosting sites and delivery networks.

“Web-based malware has become so dynamic that it is nearly impossible to protect every user from every new attack with traditional defenses,” said Steve Daheb, chief marketing officer and senior vice president at Blue Coat Systems. “With a unique comprehensive view of the Web ecosystem, Blue Coat Web security solutions can identify and track malware networks to proactively protect customers from new attacks that these networks attempt to launch.”

The firm said search engine poisoning was the most popular malware vector in the first half of 2011. The report also analyzed how and where on the Internet the users were brought into malware delivery networks. The researchers found out that in nearly 40 percent of all malware incidents, Search Engines/Portals, which unsurprisingly were also the most requested Web content during the same time period, were the entry point into malware delivery networks.

Social Networking was the fifth most popular entry point into malware delivery networks and the third most requested content. Traditional methods such as use of email and pornography were also noted during this time. Email ranked as the third most popular category of Web content which was used to drive users to a malware network. The group was, however, ranked as the 17th most requested category.

For the first half of 2011, Shnakule was the leading malware delivery network, both by size and effectiveness, the firm’s official website reported.