Researchers have cracked open a botnet that amassed more than 60GB of passwords and other stolen data, even as it cloaked itself using a state-of-the-art technique known as fast flux.
When its command-and-control server was infiltrated, the Mumba botnet had snagged more than 55,000 PCs, according to the researchers from anti-virus provider AVG. The data-stealing operation is the work of the notorious Avalanche Group, a criminal operation that was responsible for two-thirds of all phishing attacks in the second half of 2009, according to a report earlier this year from the Anti-Phishing Working Group.
“These criminals are some of the most sophisticated on the internet, and have perfected a mass-production system for deploying phishing sites and 'crimeware,'” AVG wrote in a report issued Monday. “This means that mitigating the threat by going after the servers hosting the data using the 'Mumba' botnet is now much harder than before.”
Most botnet command-and-control channels run on compromised webservers or web-hosting services designed for criminals, making it possible to dismantle the network by taking down the central server. Mumba, by contrast, makes use of fast-flux technology, in which the operations are carried out on thousands of compromised PCs. That allows the IP address and host machine to change every few minutes, a measure that frequently foils takedown attempts by researchers and law enforcement.
The botnet appears to have been spawned with an initial malware campaign that was launched in April. Its first week saw more than 35,000 infections. Several smaller campaigns were responsible for the remainder of the botnet's 55,000 victims. The malware uses at least four variants of the latest Zeus crimeware kit, which allows well-financed criminals to deploy highly sophisticated botnets in a hurry.
AVG's discovery is only the latest time that researchers have been able to penetrate a rogue network built on the back of Zeus. Earlier this year, researchers with a separate firm got inside a network that had compromised more than 74,000 machines from at least 2,500 companies, many of which were Fortune 500 firms.
Both botnets were adept at stealing highly sensitive personal details from the PCs they compromised. The stolen data includes login credentials for online bank, retail, and email accounts, and social-networking sites.
A PDF of AVG's report is here. ®