evention systems.Phishers are also attempting to bypass filtering technologies by creatingmultiple randomized messages and distributing those messages is a broaduncontrolled fashion. During the first six months of 2006, 157,477 uniquephishing messages were detected, marking an increase of 81 percent over the previous period. At the same time, spam made up 54 percent of all monitorede-mail traffic, a slight increase from 50 percent the previous period. Mostspammers are opting to exclude malicious code with their spam to decrease the chances of being blocked and instead include links to Web sites hostingmalicious code. Financial Gain Drives Malicious Activity Financial gain remains the motivation behind many of the threats during thereporting period. For example, bot networks can be used not only to spreadmalicious code, but to send spam or phishing messages, download adware andspyware, attack an organization, and harvest confidential information.Symantec identified more than 4.6 million distinct, active bot networkcomputers and observed an average of 57,717 active bot network computersper day during this period. Bot networks are also commonly used indenial-of-service (DoS) attacks, a major threat to organizations as theseattacks can result in the disruption of communication, loss of revenue,damage to brand and reputation, and exposure to criminal extortion schemes. During the first half of 2006, Symantec observed an average of 6,110 DoSattacks per day. Other financially motivated attacks use modular malicious code, malwarethat updates itself or downloads a more aggressive threat upon establishinga foothold on the victim host, to expose sensitive information. During thefirst half of 2006, modular malicious code accounted for 79 percent of thetop 50 malicious code reported to Symantec. Additionally, malicious code threats that expose confidential data represented 30 of the top 50 samples submitted to Symantec. For the first time, Symantec tracked the sectors of brands being targeted by phishing attacks ? another means to monetary gain. Not surprisingly, thefinancial services sector was the most heavily phished, accounting for 84percent of phishing sites tracked by the Symantec Phish Report Network andSymantec Brightmail AntiSpam this period. Additional Key Findings