Botnets powered by residential proxy networks are proliferating, enabling cybercriminals of all types to evade detection by blending in with seemingly legitimate traffic, Lumen Technology’s Black Lotus Labs said in a report Friday.

The global scale of botnets observed by Lumen is currently approaching 60 million victim IP addresses, Chris Formosa, senior lead information security engineer at Black Lotus Labs, told CyberScoop. Roughly 1 in 4 of those compromised IPs are based in the United States, and the true number of infected devices is much greater because there are networks beyond Lumen’s visibility and multiple devices are often unknowingly running a malicious proxy network on the same IP. 

Super-sized botnets are also gaining momentum, according to Lumen, with an average of 10 distinct botnets controlling their own populations of about 1 million active victims daily.

“The only reason these botnets keep getting more and more victims is because there is clearly a market. Aside from criminal activity, who wants access to millions of IPs regularly?” Formosa said. 

That demand for botnets fuels opportunities for growth, reselling, collaboration, and quick rebounds following massive disruptions.

IPIDEA, one of the largest residential proxy networks in operation when its infrastructure was disrupted by coordinated strikes in January, recovered at nearly half-strength within hours and earlier this surpassed its pre-disruption botnet size with a current botnet population of about 10 million IPs, researchers said.

“Their rebuild was eye-opening as they began to rebound from that interdiction,” Ryan English, information security engineer at Black Lotus Labs, told CyberScoop. “Even for how quickly some botnets can rebound, theirs was surprising. We’ve seen them all rebuild, but we haven’t seen anybody do it that fast.”

Meanwhile, botnets are continuously growing, as cybercriminals seek out the cover they provide, more cheap and poorly defended devices hit the market and vendors stop providing security updates for older but still usable products. 

“Your available pool for those proxy hunters grows every year, and it will continue to grow every year,” English said, adding that more than 1 billion devices are currently vulnerable and available to be unknowingly sucked up into botnets.

The challenge for defenders is lopsided, and while disruptions and seizures occur relatively often, botnet operators have formed a global supply chain with pathways that are difficult to break. 

“We have observed multiple residential proxy services collaborating to form what amounts to the largest cooperative network ever seen on the internet,” researchers wrote in the report.

Black Lotus Labs currently tracks more than 30 distinct malicious proxy botnet clusters, and most of those regularly boast more than 100,000 daily victims.

“Our understanding of the various botnets in this space, along with experience in multiple disruptions, leads us to a very important conclusion: taking down a single malicious proxy provider or their botnet in isolation is likely to result in a short-lived solution,” researchers wrote. 

“In recent years, the malicious proxy environment has essentially created the largest collective botnet currently active on the internet, capable of moving millions of IPs within hours to wherever they are needed,” they added. “Until the malicious proxy landscape is properly addressed and regulated on both the private industry and law enforcement sides, this issue will grow and, along with the DDoS botnet landscape, will most likely become a greater problem in the long term.”

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In a novel maneuver for a disruption operation against cyber attackers, industry and law enforcement teamed up to conduct a court takedown of two widely-used criminal tools at once rather than individually, Microsoft said Tuesday.

The takedown simultaneously went after Amadey, a botnet that can serve as a malware delivery system, and StealC, an infostealer. Cybercriminals often use them in conjunction and they rely on the same infrastructure, Microsoft said.

“When multiple parts of an operation are disrupted together, attacks are harder to launch, scale, and recover from,” said Steven Masada, assistant general counsel for Microsoft’s Digital Crimes Unit. “The result: fewer disrupted services, fewer opportunities for cybercriminals to profit, and more friction when they try to rebuild. It’s no longer enough to go after threats one by one. We need to interrupt how the attacks are put together.”

Microsoft had been tracking Amadey with ESET, BitSight, Lumen and Mitsui Bussan Secure Directions. Meanwhile, Europol had been investigating StealC alongside law enforcement partners including Germany’s Federal Criminal Police Office and the Dutch and Danish National Police as well as IBM X-Force and Proofpoint.

They then joined forces and turned to the Racketeer Influenced and Corrupt Organizations (RICO) Act, used to help authorities go after organized crime, to disrupt more than 200 command-and-control servers. Microsoft said it gained insights from its artificial intelligence product Copilot that “allowed the legal team to treat both malware families as part of a single criminal conspiracy.”

Microsoft regularly leads court-authorized disruption operations, but the industry and law enforcement partnerships combined with AI to expand data collection and identify connections beyond what one company could normally do, it said.

Amadey and StealC were linked to more than 140,000 infected computers around the globe in the first week of May alone, the company said. StealC has ranked among the top infostealers for years since its emergence in 2023 and sells in underground forums as a malware-as-a-service. It’s typically used by Russia-linked groups.

Amadey dates back to 2018, and is also commonly employed by Russian groups, including in attacks on Ukraine.

Their interaction shows the assembly line-like structure of modern cybercrime, Microsoft said. Even if the cybercriminals behind both tools never coordinate, their tools are designed to work together, it said.

“StealC is an infostealer that collects sensitive data from browsers, cryptocurrency wallets, messaging applications, email clients, and gaming platforms,” the company wrote in a separate blog post. “It is a malware-as-a-service (MaaS) offering that threat actors use to generate customized payloads and manage stolen data through a centralized web panel. Meanwhile, Amadey is a MaaS loader that threat actors use to deliver StealC and other malware. Modular, pay-as-you-go models like StealC and Amadey allow threat actors to use a single initial infection to quickly escalate into multiple other threats.”

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The FBI, along with Google and Lumen Technologies, took down a major cybercrime network based in China that was responsible for an estimated $1.9 billion in losses, officials said Friday. 

Outsider, which provided phishing kits and hosted infrastructure for cybercriminals since July 2023, facilitated a wave of phishing attacks against people and businesses in 55 countries, including the United States, the FBI said in a LinkedIn post.

The jointly coordinated effort dubbed “Operation Ghost Hook” netted the seizure of several domains of the group’s core admin servers, a Shopify storefront, roughly $100,000 from Outsider payment wallets and thousands of domains registered through U.S.-based providers, officials said.

The FBI said it also used an Outsider Telegram bot to access information on the cybercrime network’s customers.

“The criminals behind Outsider Enterprise built a business out of impersonating trusted brands to defraud hundreds of thousands of victims,” Brett Leatherman, assistant director of the FBI’s cyber division, said in a statement.

Authorities traced Outsider’s phishing domains to nearly 3.9 million stolen credit cards.

Google, one of the vendors impersonated by the phishing kits, described Outsider as a massive AI-powered operation. 

Outsider provided its phishing kit, which allowed cybercriminals to create fake sites and phishing campaigns to steal credit cards, bank account credentials and personal data, for a weekly subscription as low as $88 per week, the company said in a civil lawsuit it filed to dismantle the cybercrime network’s infrastructure. 

The China-based group behind the operation encouraged and provided step-by-step instructions for customers to use Gemini and other AI platforms to generate custom code for phishing lures and corresponding sites for illegitimate missed packages, overdue highway tolls, parking violations, issues with a brokerage account or wireless carrier rewards.

“The Outsider software allows scammers to request multiple types of verification from victims, including SMS, PIN, email and app verification,” Google wrote in the lawsuit filed in the U.S. District for the Southern District of New York. “This flexibility enables the enterprise to defeat various forms of authentication security.”

Google said it’s working with AT&T, T-Mobile and Verizon to intercept the spam messages before they reach customers, but these types of phishing attacks are prevalent and have been spreading for years. 

Google is also pushing for legislative action, including a series of bills, to combat these scams, General Counsel Halimah DeLaine Prado wrote in a blog post.

“Litigation alone won’t end this,” she wrote. “As threats evolve, our laws must, too.”

Google said it doesn’t know the real names of the people or entities involved in Outsider, but said the operation is supported by multiple cybercrime groups providing different roles with overlapping infrastructure.

The FBI said the takedown was part of Operation Riptide, an ongoing campaign targeting cybercriminals and the infrastructure and financial networks they use to commit fraud.

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