San Francisco—As corporations team up with cops to take down criminals' networks, the operators behind banking botnets have expanded beyond major financial institutions to hit smaller banks as well as other targets, such as corporate accounting and payroll systems, according to a report released here on April 22 at the RSA Conference by managed security firm Dell Secureworks.
The Dyre botnet, for example, appeared following the takedown of the Gameover Zeus botnet, evolving from a rudimentary banking trojan to advanced modular malware used in more than 20 campaigns targeting more than 432 financial institutions. In May 2014, the FBI, security firms and international law enforcement moved against the Gameover Zeus botnet and took down the operation that had compromised approximately 500,000 to 1 million computers and caused an estimated $100 million in damages.
Since the takedown, bot operators have begun to change their tactics, Pallav Khandhar, senior security researcher with Dell Secureworks, told eWEEK.
"After the Gameover Zeus takedown, they have definitely learned a few things," he said. "They are using anonymizing services to hide their infrastructure, and they are also targeting accounting and payroll services and even social networking."
Overall, the top-13 banking botnets targeted more than 1,400 financial institutions, according to the report.
In the past year, law enforcement agencies have teamed up with security firms to take down five botnets. In addition to the takedown of Gameover Zeus, dubbed Operation Tovar by the FBI, companies have teamed with international law-enforcement agencies to disrupt the Shylock, Ramnit, Beebone and Simda botnets. An increasing number of countries have made international transactions more difficult, as well.
The law enforcement activities and changes in financial procedures have caused criminal operators to change their own tactics.
In the past, some enterprising criminal groups would sell access to or lease out their botnets, but as law enforcement scrutiny heats up, the groups are creating smaller, private botnets. Dyre and Bugat, for example, have added the capability to send out spam, rather than using leased spam botnets.
"Especially after the Gameover Zeus takedown, many groups no longer want to work with each other," Khandhar said.
The advancements in Dyre show how criminals are adapting. The first variant of Dyre ran for less than 24 hours, conducting a few spam campaigns before disappearing for three weeks. Following that, far superior variants of the malware appeared, with the ability to download different modules to add functionality.
"When it came out first, they were likely doing a test run to see the reaction from the security community," said Khandhar.