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KrebsOnSecurity last week was hit by a near record distributed denial-of-service (DDoS) attack that clocked in at more than 6.3 terabits of data per second (a terabit is one trillion bits of data). The brief attack appears to have been a test run for a massive new Internet of Things (IoT) botnet capable of launching crippling digital assaults that few web destinations can withstand. Read on for more about the botnet, the attack, and the apparent creator of this global menace.
For reference, the 6.3 Tbps attack last week was ten times the size of the assault launched against this site in 2016 by the Mirai IoT botnet, which held KrebsOnSecurity offline for nearly four days. The 2016 assault was so large that Akamai – which was providing pro-bono DDoS protection for KrebsOnSecurity at the time — asked me to leave their service because the attack was causing problems for their paying customers.
Since the Mirai attack, KrebsOnSecurity.com has been behind the protection of Project Shield, a free DDoS defense service that Google provides to websites offering news, human rights, and election-related content. Google Security Engineer Damian Menscher told KrebsOnSecurity the May 12 attack was the largest Google has ever handled. In terms of sheer size, it is second only to a very similar attack that Cloudflare mitigated and wrote about in April.
After comparing notes with Cloudflare, Menscher said the botnet that launched both attacks bears the fingerprints of Aisuru, a digital siege machine that first surfaced less than a year ago. Menscher said the attack on KrebsOnSecurity lasted less than a minute, hurling large UDP data packets at random ports at a rate of approximately 585 million data packets per second.
“It was the type of attack normally designed to overwhelm network links,” Menscher said, referring to the throughput connections between and among various Internet service providers (ISPs). “For most companies, this size of attack would kill them.”
A graph depicting the 6.5 Tbps attack mitigated by Cloudflare in April 2025. Image: Cloudflare.
The Aisuru botnet comprises a globally-dispersed collection of hacked IoT devices, including routers, digital video recorders and other systems that are commandeered via default passwords or software vulnerabilities. As documented by researchers at QiAnXin XLab, the botnet was first identified in an August 2024 attack on a large gaming platform.
Aisuru reportedly went quiet after that exposure, only to reappear in November with even more firepower and software exploits. In a January 2025 report, XLab found the new and improved Aisuru (a.k.a. “Airashi“) had incorporated a previously unknown zero-day vulnerability in Cambium Networks cnPilot routers.
The people behind the Aisuru botnet have been peddling access to their DDoS machine in public Telegram chat channels that are closely monitored by multiple security firms. In August 2024, the botnet was rented out in subscription tiers ranging from $150 per day to $600 per week, offering attacks of up to two terabits per second.
“You may not attack any measurement walls, healthcare facilities, schools or government sites,” read a notice posted on Telegram by the Aisuru botnet owners in August 2024.
Interested parties were told to contact the Telegram handle “@yfork” to purchase a subscription. The account @yfork previously used the nickname “Forky,” an identity that has been posting to public DDoS-focused Telegram channels since 2021.
According to the FBI, Forky’s DDoS-for-hire domains have been seized in multiple law enforcement operations over the years. Last year, Forky said on Telegram he was selling the domain stresser[.]best, which saw its servers seized by the FBI in 2022 as part of an ongoing international law enforcement effort aimed at diminishing the supply of and demand for DDoS-for-hire services.
“The operator of this service, who calls himself ‘Forky,’ operates a Telegram channel to advertise features and communicate with current and prospective DDoS customers,” reads an FBI seizure warrant (PDF) issued for stresser[.]best. The FBI warrant stated that on the same day the seizures were announced, Forky posted a link to a story on this blog that detailed the domain seizure operation, adding the comment, “We are buying our new domains right now.”
A screenshot from the FBI’s seizure warrant for Forky’s DDoS-for-hire domains shows Forky announcing the resurrection of their service at new domains.
Approximately ten hours later, Forky posted again, including a screenshot of the stresser[.]best user dashboard, instructing customers to use their saved passwords for the old website on the new one.
A review of Forky’s posts to public Telegram channels — as indexed by the cyber intelligence firms Unit 221B and Flashpoint — reveals a 21-year-old individual who claims to reside in Brazil [full disclosure: Flashpoint is currently an advertiser on this blog].
Since late 2022, Forky’s posts have frequently promoted a DDoS mitigation company and ISP that he operates called botshield[.]io. The Botshield website is connected to a business entity registered in the United Kingdom called Botshield LTD, which lists a 21-year-old woman from Sao Paulo, Brazil as the director. Internet routing records indicate Botshield (AS213613) currently controls several hundred Internet addresses that were allocated to the company earlier this year.
Domaintools.com reports that botshield[.]io was registered in July 2022 to a Kaike Southier Leite in Sao Paulo. A LinkedIn profile by the same name says this individual is a network specialist from Brazil who works in “the planning and implementation of robust network infrastructures, with a focus on security, DDoS mitigation, colocation and cloud server services.”
Image: Jaclyn Vernace / Shutterstock.com.
In his posts to public Telegram chat channels, Forky has hardly attempted to conceal his whereabouts or identity. In countless chat conversations indexed by Unit 221B, Forky could be seen talking about everyday life in Brazil, often remarking on the extremely low or high prices in Brazil for a range of goods, from computer and networking gear to narcotics and food.
Reached via Telegram, Forky claimed he was “not involved in this type of illegal actions for years now,” and that the project had been taken over by other unspecified developers. Forky initially told KrebsOnSecurity he had been out of the botnet scene for years, only to concede this wasn’t true when presented with public posts on Telegram from late last year that clearly showed otherwise.
Forky denied being involved in the attack on KrebsOnSecurity, but acknowledged that he helped to develop and market the Aisuru botnet. Forky claims he is now merely a staff member for the Aisuru botnet team, and that he stopped running the botnet roughly two months ago after starting a family. Forky also said the woman named as director of Botshield is related to him.
Forky offered equivocal, evasive responses to a number of questions about the Aisuru botnet and his business endeavors. But on one point he was crystal clear:
“I have zero fear about you, the FBI, or Interpol,” Forky said, asserting that he is now almost entirely focused on their hosting business — Botshield.
Forky declined to discuss the makeup of his ISP’s clientele, or to clarify whether Botshield was more of a hosting provider or a DDoS mitigation firm. However, Forky has posted on Telegram about Botshield successfully mitigating large DDoS attacks launched against other DDoS-for-hire services.
DomainTools finds the same Sao Paulo street address in the registration records for botshield[.]io was used to register several other domains, including cant-mitigate[.]us. The email address in the WHOIS records for that domain is forkcontato@gmail.com, which DomainTools says was used to register the domain for the now-defunct DDoS-for-hire service stresser[.]us, one of the domains seized in the FBI’s 2023 crackdown.
On May 8, 2023, the U.S. Department of Justice announced the seizure of stresser[.]us, along with a dozen other domains offering DDoS services. The DOJ said ten of the 13 domains were reincarnations of services that were seized during a prior sweep in December, which targeted 48 top stresser services (also known as “booters”).
Forky claimed he could find out who attacked my site with Aisuru. But when pressed a day later on the question, Forky said he’d come up empty-handed.
“I tried to ask around, all the big guys are not retarded enough to attack you,” Forky explained in an interview on Telegram. “I didn’t have anything to do with it. But you are welcome to write the story and try to put the blame on me.”
The 6.3 Tbps attack last week caused no visible disruption to this site, in part because it was so brief — lasting approximately 45 seconds. DDoS attacks of such magnitude and brevity typically are produced when botnet operators wish to test or demonstrate their firepower for the benefit of potential buyers. Indeed, Google’s Menscher said it is likely that both the May 12 attack and the slightly larger 6.5 Tbps attack against Cloudflare last month were simply tests of the same botnet’s capabilities.
In many ways, the threat posed by the Aisuru/Airashi botnet is reminiscent of Mirai, an innovative IoT malware strain that emerged in the summer of 2016 and successfully out-competed virtually all other IoT malware strains in existence at the time.
As first revealed by KrebsOnSecurity in January 2017, the Mirai authors were two U.S. men who co-ran a DDoS mitigation service — even as they were selling far more lucrative DDoS-for-hire services using the most powerful botnet on the planet.
Less than a week after the Mirai botnet was used in a days-long DDoS against KrebsOnSecurity, the Mirai authors published the source code to their botnet so that they would not be the only ones in possession of it in the event of their arrest by federal investigators.
Ironically, the leaking of the Mirai source is precisely what led to the eventual unmasking and arrest of the Mirai authors, who went on to serve probation sentences that required them to consult with FBI investigators on DDoS investigations. But that leak also rapidly led to the creation of dozens of Mirai botnet clones, many of which were harnessed to fuel their own powerful DDoS-for-hire services.
Menscher told KrebsOnSecurity that as counterintuitive as it may sound, the Internet as a whole would probably be better off if the source code for Aisuru became public knowledge. After all, he said, the people behind Aisuru are in constant competition with other IoT botnet operators who are all striving to commandeer a finite number of vulnerable IoT devices globally.
Such a development would almost certainly cause a proliferation of Aisuru botnet clones, he said, but at least then the overall firepower from each individual botnet would be greatly diminished — or at least within range of the mitigation capabilities of most DDoS protection providers.
Barring a source code leak, Menscher said, it would be nice if someone published the full list of software exploits being used by the Aisuru operators to grow their botnet so quickly.
“Part of the reason Mirai was so dangerous was that it effectively took out competing botnets,” he said. “This attack somehow managed to compromise all these boxes that nobody else knows about. Ideally, we’d want to see that fragmented out, so that no [individual botnet operator] controls too much.”
The U.S. government on Wednesday announced the arrest and charging of two Sudanese brothers accused of running Anonymous Sudan (a.k.a. AnonSudan), a cybercrime business known for launching powerful distributed denial-of-service (DDoS) attacks against a range of targets, including dozens of hospitals, news websites and cloud providers. The younger brother is facing charges that could land him life in prison for allegedly seeking to kill people with his attacks.
Image: FBI
Active since at least January 2023, AnonSudan has been described in media reports as a “hacktivist” group motivated by ideological causes. But in a criminal complaint, the FBI said those high-profile cyberattacks were effectively commercials for the hackers’ DDoS-for-hire service, which they sold to paying customers for as little as $150 a day — with up to 100 attacks allowed per day — or $700 for an entire week.
The complaint says despite reports suggesting Anonymous Sudan might be state-sponsored Russian actors pretending to be Sudanese hackers with Islamist motivations, AnonSudan was led by two brothers in Sudan — Ahmed Salah Yousif Omer, 22, and Alaa Salah Yusuuf Omer, 27.
AnonSudan claimed credit for successful DDoS attacks on numerous U.S. companies, causing a multi-day outage for Microsoft’s cloud services in June 2023. The group hit PayPal the following month, followed by Twitter/X (Aug. 2023), and OpenAI (Nov. 2023). An indictment in the Central District of California notes the duo even swamped the websites of the FBI and the Department of State.
Prosecutors say Anonymous Sudan offered a “Limited Internet Shutdown Package,” which would enable customers to shut down internet service providers in specified countries for $500 (USD) an hour. The two men also allegedly extorted some of their victims for money in exchange for calling off DDoS attacks.
The government isn’t saying where the Omer brothers are being held, only that they were arrested in March 2024 and have been in custody since. A statement by the U.S. Department of Justice says the government also seized control of AnonSudan’s DDoS infrastructure and servers after the two were arrested in March.
AnonSudan accepted orders over the instant messaging service Telegram, and marketed its DDoS service by several names, including “Skynet,” “InfraShutdown,” and the “Godzilla botnet.” However, the DDoS machine the Omer brothers allegedly built was not made up of hacked devices — as is typical with DDoS botnets.
Instead, the government alleges Skynet was more like a “distributed cloud attack tool,” with a command and control (C2) server, and an entire fleet of cloud-based servers that forwards C2 instructions to an array of open proxy resolvers run by unaffiliated third parties, which then transmit the DDoS attack data to the victims.
Amazon was among many companies credited with helping the government in the investigation, and said AnonSudan launched its attacks by finding hosting companies that would rent them small armies of servers.
“Where their potential impact becomes really significant is when they then acquire access to thousands of other machines — typically misconfigured web servers — through which almost anyone can funnel attack traffic,” Amazon explained in a blog post. “This extra layer of machines usually hides the true source of an attack from the targets.”
The security firm CrowdStrike said the success of AnonSudan’s DDoS attacks stemmed from a combination of factors, including sophisticated techniques for bypassing DDoS mitigation services. Also, AnonSudan typically launched so-called “Layer 7” attacks that sought to overwhelm targeted “API endpoints” — the back end systems responsible for handling website requests — with bogus requests for data, leaving the target unable to serve legitimate visitors.
The Omer brothers were both charged with one count of conspiracy to damage protected computers. The younger brother — Ahmed Salah — was also charged with three counts of damaging protected computers.
A passport for Ahmed Salah Yousif Omer. Image: FBI.
If extradited to the United States, tried and convicted in a court of law, the older brother Alaa Salah would be facing a maximum of five years in prison. But prosecutors say Ahmed Salah could face life in prison for allegedly launching attacks that sought to kill people.
As Hamas fighters broke through the border fence and attacked Israel on Oct. 7, 2023, a wave of rockets was launched into Israel. At the same time, AnonSudan announced it was attacking the APIs that power Israel’s widely-used “red alert” mobile apps that warn residents about any incoming rocket attacks in their area.
In February 2024, AnonSudan launched a digital assault on the Cedars-Sinai Hospital in the Los Angeles area, an attack that caused emergency services and patients to be temporarily redirected to different hospitals.
The complaint alleges that in September 2023, AnonSudan began a week-long DDoS attack against the Internet infrastructure of Kenya, knocking offline government services, banks, universities and at least seven hospitals.
Malicious hackers are exploiting a zero-day vulnerability in Versa Director, a software product used by many Internet and IT service providers. Researchers believe the activity is linked to Volt Typhoon, a Chinese cyber espionage group focused on infiltrating critical U.S. networks and laying the groundwork for the ability to disrupt communications between the United States and Asia during any future armed conflict with China.
Image: Shutterstock.com
Versa Director systems are primarily used by Internet service providers (ISPs), as well as managed service providers (MSPs) that cater to the IT needs of many small to mid-sized businesses simultaneously. In a security advisory published Aug. 26, Versa urged customers to deploy a patch for the vulnerability (CVE-2024-39717), which the company said is fixed in Versa Director 22.1.4 or later.
Versa said the weakness allows attackers to upload a file of their choosing to vulnerable systems. The advisory placed much of the blame on Versa customers who “failed to implement system hardening and firewall guidelines…leaving a management port exposed on the internet that provided the threat actors with initial access.”
Versa’s advisory doesn’t say how it learned of the zero-day flaw, but its vulnerability listing at mitre.org acknowledges “there are reports of others based on backbone telemetry observations of a 3rd party provider, however these are unconfirmed to date.”
Those third-party reports came in late June 2024 from Michael Horka, senior lead information security engineer at Black Lotus Labs, the security research arm of Lumen Technologies, which operates one of the global Internet’s largest backbones.
In an interview with KrebsOnSecurity, Horka said Black Lotus Labs identified a web-based backdoor on Versa Director systems belonging to four U.S. victims and one non-U.S. victim in the ISP and MSP sectors, with the earliest known exploit activity occurring at a U.S. ISP on June 12, 2024.
“This makes Versa Director a lucrative target for advanced persistent threat (APT) actors who would want to view or control network infrastructure at scale, or pivot into additional (or downstream) networks of interest,” Horka wrote in a blog post published today.
Black Lotus Labs said it assessed with “medium” confidence that Volt Typhoon was responsible for the compromises, noting the intrusions bear the hallmarks of the Chinese state-sponsored espionage group — including zero-day attacks targeting IT infrastructure providers, and Java-based backdoors that run in memory only.
In May 2023, the National Security Agency (NSA), the Federal Bureau of Investigation (FBI), and the Cybersecurity Infrastructure Security Agency (CISA) issued a joint warning (PDF) about Volt Typhoon, also known as “Bronze Silhouette” and “Insidious Taurus,” which described how the group uses small office/home office (SOHO) network devices to hide their activity.
In early December 2023, Black Lotus Labs published its findings on “KV-botnet,” thousands of compromised SOHO routers that were chained together to form a covert data transfer network supporting various Chinese state-sponsored hacking groups, including Volt Typhoon.
In January 2024, the U.S. Department of Justice disclosed the FBI had executed a court-authorized takedown of the KV-botnet shortly before Black Lotus Labs released its December report.
In February 2024, CISA again joined the FBI and NSA in warning Volt Typhoon had compromised the IT environments of multiple critical infrastructure organizations — primarily in communications, energy, transportation systems, and water and wastewater sectors — in the continental and non-continental United States and its territories, including Guam.
“Volt Typhoon’s choice of targets and pattern of behavior is not consistent with traditional cyber espionage or intelligence gathering operations, and the U.S. authoring agencies assess with high confidence that Volt Typhoon actors are pre-positioning themselves on IT networks to enable lateral movement to OT [operational technology] assets to disrupt functions,” that alert warned.
In a speech at Vanderbilt University in April, FBI Director Christopher Wray said China is developing the “ability to physically wreak havoc on our critical infrastructure at a time of its choosing,” and that China’s plan is to “land blows against civilian infrastructure to try to induce panic.”
Ryan English, an information security engineer at Lumen, said it’s disappointing his employer didn’t at least garner an honorable mention in Versa’s security advisory. But he said he’s glad there are now a lot fewer Versa systems exposed to this attack.
“Lumen has for the last nine weeks been very intimate with their leadership with the goal in mind of helping them mitigate this,” English said. “We’ve given them everything we could along the way, so it kind of sucks being referenced just as a third party.”
A 26-year-old Finnish man was sentenced to more than six years in prison today after being convicted of hacking into an online psychotherapy clinic, leaking tens of thousands of patient therapy records, and attempting to extort the clinic and patients.
On October 21, 2020, the Vastaamo Psychotherapy Center in Finland became the target of blackmail when a tormentor identified as “ransom_man” demanded payment of 40 bitcoins (~450,000 euros at the time) in return for a promise not to publish highly sensitive therapy session notes Vastaamo had exposed online.
Ransom_man announced on the dark web that he would start publishing 100 patient profiles every 24 hours. When Vastaamo declined to pay, ransom_man shifted to extorting individual patients. According to Finnish police, some 22,000 victims reported extortion attempts targeting them personally, targeted emails that threatened to publish their therapy notes online unless paid a 500 euro ransom.
Finnish prosecutors quickly zeroed in on a suspect: Julius “Zeekill” Kivimäki, a notorious criminal hacker convicted of committing tens of thousands of cybercrimes before he became an adult. After being charged with the attack in October 2022, Kivimäki fled the country. He was arrested four months later in France, hiding out under an assumed name and passport.
Antti Kurittu is a former criminal investigator who worked on an investigation involving Kivimäki’s use of the Zbot botnet, among other activities Kivimäki engaged in as a member of the hacker group Hack the Planet (HTP).
Kurittu said the prosecution had demanded at least seven years in jail, and that the sentence handed down was six years and three months. Kurittu said prosecutors knocked a few months off of Kivimäki’s sentence because he agreed to pay compensation to his victims, and that Kivimäki will remain in prison during any appeal process.
“I think the sentencing was as expected, knowing the Finnish judicial system,” Kurittu told KrebsOnSecurity. “As Kivimäki has not been sentenced to a non-suspended prison sentence during the last five years, he will be treated as a first-timer, his previous convictions notwithstanding.”
But because juvenile convictions in Finland don’t count towards determining whether somebody is a first-time offender, Kivimäki will end up serving approximately half of his sentence.
“This seems like a short sentence when taking into account the gravity of his actions and the life-altering consequences to thousands of people, but it’s almost the maximum the law allows for,” Kurittu said.
Kivimäki initially gained notoriety as a self-professed member of the Lizard Squad, a mainly low-skilled hacker group that specialized in DDoS attacks. But American and Finnish investigators say Kivimäki’s involvement in cybercrime dates back to at least 2008, when he was introduced to a founding member of what would soon become HTP.
Finnish police said Kivimäki also used the nicknames “Ryan”, “RyanC” and “Ryan Cleary” (Ryan Cleary was actually a member of a rival hacker group — LulzSec — who was sentenced to prison for hacking).
Kivimäki and other HTP members were involved in mass-compromising web servers using known vulnerabilities, and by 2012 Kivimäki’s alias Ryan Cleary was selling access to those servers in the form of a DDoS-for-hire service. Kivimäki was 15 years old at the time.
In 2013, investigators going through devices seized from Kivimäki found computer code that had been used to crack more than 60,000 web servers using a previously unknown vulnerability in Adobe’s ColdFusion software. KrebsOnSecurity detailed the work of HTP in September 2013, after the group compromised servers inside data brokers LexisNexis, Kroll, and Dun & Bradstreet.
The group used the same ColdFusion flaws to break into the National White Collar Crime Center (NWC3), a non-profit that provides research and investigative support to the U.S. Federal Bureau of Investigation (FBI).
As KrebsOnSecurity reported at the time, this small ColdFusion botnet of data broker servers was being controlled by the same cybercriminals who’d assumed control over SSNDOB, which operated one of the underground’s most reliable services for obtaining Social Security Number, dates of birth and credit file information on U.S. residents.
Kivimäki was responsible for making an August 2014 bomb threat against former Sony Online Entertainment President John Smedley that grounded an American Airlines plane. Kivimäki also was involved in calling in multiple fake bomb threats and “swatting” incidents — reporting fake hostage situations at an address to prompt a heavily armed police response to that location.
Ville Tapio, the former CEO of Vastaamo, was fired and also prosecuted following the breach. Ransom_man bragged about Vastaamo’s sloppy security, noting the company had used the laughably weak username and password “root/root” to protect sensitive patient records.
Investigators later found Vastaamo had originally been hacked in 2018 and again in 2019. In April 2023, a Finnish court handed down a three-month sentence for Tapio, but that sentence was suspended because he had no previous criminal record.
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