There were 23,000 new cases of Web Based Malware in the first quarter of 2007, compared with 9,000 in the first quarter of 2006. This represents an increase of approximately 150%. 70% of infected web pages were legitimate sites that had been hacked (recent, high profile examples are the Circuit City, Dolphins Stadium web sites). The increase coincides with a shift in tactics used by malware propogators to infect unsuspecting surfers. In addition to hacking/infecting popular, heavily visited sites, Bot herders are inserting links to malware infected sites in spam email. Another tactic used by malware authors is the use of Google PPC ads to lure surfers to malware infected web sites.