Number of malware infected sites has nearly doubled

Malvertising, advertising containing malware, also is on the rise, with impressions doubling to 3 million per day from the third quarter of 2010, Dasient said in a blog post.

"The probability that an average Internet user will hit an infected page after three months of Web browsing is 95 percent," the company said.

The news corresponds with information released this week by another security firm. An analysis of than 3,000 Web sites across 400 organizations last year found that 44 percent of them had serious vulnerabilities at all times, while 24 percent were frequently vulnerable for an average of at least 270 days a year, according to WhiteHat Security, which provides Web site testing and security services for companies. Meanwhile, only 16 percent of the sites examined were found to be rarely vulnerable, the report said.