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Criminals shifted away from building up botnet armies in favor of launching targeted attacks on specific corporate networks in 2011, according to security researchers.

The overall number of networks and computers hijacked by criminals globally and commandeered into a botnet army has declined each year since 2009, Cisco said in its 2011 state of security report, released Dec. 14. The Global Adversary Resource Market Share Index, which tracks the number of compromised systems, has dropped over the past few years, Cisco said.

Attackers also changed how they distribute malware in 2011, as they realized it could be used for "far more nefarious purposes" than just stealing bank accounts, AppRiver researchers wrote in their 2011 review. Malware that is stealthy and "siphoning off" personal information, which can later be sold on underground markets, is potentially a more profitable approach, according to AppRiver. Facebook spammers took advantage of users’ tendency to click on links posted by "friends" to launch clickjacking scams or download malware.

"This is becoming a precision, assassin-like model versus a horrible, carpet bomb type of model," Scott Olechowski, threat research manager for Cisco, said during a Dec. 13 news conference.

Law enforcement has had success shutting down major botnets. Microsoft announced its role in shutting down Rustock botnet’s command-and-control servers located in the United States, an operation that included FireEye and federal law enforcement. Microsoft also worked with Kaspersky Lab to move against the Kelihos botnet.

"Almost immediately the effects of the operation were noticed as the millions of bots infected with Rustock stopped receiving orders and fell silent," AppRiver researchers wrote in their report, adding that with the spam-spewing botnet crippled, spam volumes have dropped nearly 35 percent in 2011.

Cisco Security also noted the decrease in spam, reporting a "steep decline" in spam volume since August 2010 from 379 billion messages a day to 124 billion. The United States was the No. 1 source for spam in 2010, but dropped to ninth place in 2011, according to Mary Landesman, senior security researcher at Cisco. India has taken over the top spot, according to Cisco. The amount of money generated annually from spam has also fallen by roughly half, to $500 million, Cisco said.

The drop for the United States was the result of a "huge effort by law enforcement" to shut down botnets, Landesman said.

However, Cisco also attributed the decline to the fact that cyber-criminals are changing their attack methods. While high-profile attacks from the Zeus botnet generated headlines, the most lucrative and efficient attacks this year were smaller operations on high-value targets, according to Landesman. The company reported earlier in the year that criminals were favoring targeted phishing emails over massive spam campaigns and were seeing bigger payoffs.

That’s not to say there were no mass email campaigns in 2011. Adversaries successfully tricked and compromised users as they customized campaigns to reflect world events, such as the devastating earthquake and tsunami in Japan and the death of Osama bin Laden. Spam emails claimed to have news and video for information-hungry users or they masqueraded as charities raising funds to help victims. Black hat search engine optimization tactics poisoned search results so that people looking for details were directed to Websites that downloaded malware onto the victims’ computers, giving attackers direct access.

To read the original eWeek article, click here: Spam Declined in 2011 as Criminals Shift to Targeted Attacks