Krebs on Security

Cloudflare Scrubs Aisuru Botnet from Top Domains List

For the past week, domains associated with the massive Aisuru botnet have repeatedly usurped Amazon, Apple, Google and Microsoft in Cloudflare’s public ranking of the most frequently requested websites. Cloudflare responded by redacting Aisuru domain names from their top websites list. The chief executive at Cloudflare says Aisuru’s overlords are using the botnet to boost their malicious domain rankings, while simultaneously attacking the company’s domain name system (DNS) service.

Aisuru is a rapidly growing botnet comprising hundreds of thousands of hacked Internet of Things (IoT) devices, such as poorly secured Internet routers and security cameras. The botnet has increased in size and firepower significantly since its debut in 2024, demonstrating the ability to launch record distributed denial-of-service (DDoS) attacks nearing 30 terabits of data per second.

Until recently, Aisuru’s malicious code instructed all infected systems to use DNS servers from Google — specifically, the servers at 8.8.8.8. But in early October, Aisuru switched to invoking Cloudflare’s main DNS server — 1.1.1.1 — and over the past week domains used by Aisuru to control infected systems started populating Cloudflare’s top domain rankings.

As screenshots of Aisuru domains claiming two of the Top 10 positions ping-ponged across social media, many feared this was yet another sign that an already untamable botnet was running completely amok. One Aisuru botnet domain that sat prominently for days at #1 on the list was someone’s street address in Massachusetts followed by “.com”. Other Aisuru domains mimicked those belonging to major cloud providers.

Cloudflare tried to address these security, brand confusion and privacy concerns by partially redacting the malicious domains, and adding a warning at the top of its rankings:

“Note that the top 100 domains and trending domains lists include domains with organic activity as well as domains with emerging malicious behavior.”

Cloudflare CEO Matthew Prince told KrebsOnSecurity the company’s domain ranking system is fairly simplistic, and that it merely measures the volume of DNS queries to 1.1.1.1.

“The attacker is just generating a ton of requests, maybe to influence the ranking but also to attack our DNS service,” Prince said, adding that Cloudflare has heard reports of other large public DNS services seeing similar uptick in attacks. “We’re fixing the ranking to make it smarter. And, in the meantime, redacting any sites we classify as malware.”

Renee Burton, vice president of threat intel at the DNS security firm Infoblox, said many people erroneously assumed that the skewed Cloudflare domain rankings meant there were more bot-infected devices than there were regular devices querying sites like Google and Apple and Microsoft.

“Cloudflare’s documentation is clear — they know that when it comes to ranking domains you have to make choices on how to normalize things,” Burton wrote on LinkedIn. “There are many aspects that are simply out of your control. Why is it hard? Because reasons. TTL values, caching, prefetching, architecture, load balancing. Things that have shared control between the domain owner and everything in between.”

Alex Greenland is CEO of the anti-phishing and security firm Epi. Greenland said he understands the technical reason why Aisuru botnet domains are showing up in Cloudflare’s rankings (those rankings are based on DNS query volume, not actual web visits). But he said they’re still not meant to be there.

“It’s a failure on Cloudflare’s part, and reveals a compromise of the trust and integrity of their rankings,” he said.

Greenland said Cloudflare planned for its Domain Rankings to list the most popular domains as used by human users, and it was never meant to be a raw calculation of query frequency or traffic volume going through their 1.1.1.1 DNS resolver.

“They spelled out how their popularity algorithm is designed to reflect real human use and exclude automated traffic (they said they’re good at this),” Greenland wrote on LinkedIn. “So something has evidently gone wrong internally. We should have two rankings: one representing trust and real human use, and another derived from raw DNS volume.”

Why might it be a good idea to wholly separate malicious domains from the list? Greenland notes that Cloudflare Domain Rankings see widespread use for trust and safety determination, by browsers, DNS resolvers, safe browsing APIs and things like TRANCO.

“TRANCO is a respected open source list of the top million domains, and Cloudflare Radar is one of their five data providers,” he continued. “So there can be serious knock-on effects when a malicious domain features in Cloudflare’s top 10/100/1000/million. To many people and systems, the top 10 and 100 are naively considered safe and trusted, even though algorithmically-defined top-N lists will always be somewhat crude.”

Over this past week, Cloudflare started redacting portions of the malicious Aisuru domains from its Top Domains list, leaving only their domain suffix visible. Sometime in the past 24 hours, Cloudflare appears to have begun hiding the malicious Aisuru domains entirely from the web version of that list. However, downloading a spreadsheet of the current Top 200 domains from Cloudflare Radar shows an Aisuru domain still at the very top.

According to Cloudflare’s website, the majority of DNS queries to the top Aisuru domains — nearly 52 percent — originated from the United States. This tracks with my reporting from early October, which found Aisuru was drawing most of its firepower from IoT devices hosted on U.S. Internet providers like AT&T, Comcast and Verizon.

Experts tracking Aisuru say the botnet relies on well more than a hundred control servers, and that for the moment at least most of those domains are registered in the .su top-level domain (TLD). Dot-su is the TLD assigned to the former Soviet Union (.su’s Wikipedia page says the TLD was created just 15 months before the fall of the Berlin wall).

A Cloudflare blog post from October 27 found that .su had the highest “DNS magnitude” of any TLD, referring to a metric estimating the popularity of a TLD based on the number of unique networks querying Cloudflare’s 1.1.1.1 resolver. The report concluded that the top .su hostnames were associated with a popular online world-building game, and that more than half of the queries for that TLD came from the United States, Brazil and Germany [it’s worth noting that servers for the world-building game Minecraft were some of Aisuru’s most frequent targets].

A simple and crude way to detect Aisuru bot activity on a network may be to set an alert on any systems attempting to contact domains ending in .su. This TLD is frequently abused for cybercrime and by cybercrime forums and services, and blocking access to it entirely is unlikely to raise any legitimate complaints.

Krebs on Security

Inside a Dark Adtech Empire Fed by Fake CAPTCHAs

Late last year, security researchers made a startling discovery: Kremlin-backed disinformation campaigns were bypassing moderation on social media platforms by leveraging the same malicious advertising technology that powers a sprawling ecosystem of online hucksters and website hackers. A new report on the fallout from that investigation finds this dark ad tech industry is far more resilient and incestuous than previously known.

In November 2024, researchers at the security firm Qurium published an investigation into “Doppelganger,” a disinformation network that promotes pro-Russian narratives and infiltrates Europe’s media landscape by pushing fake news through a network of cloned websites.

Doppelganger campaigns use specialized links that bounce the visitor’s browser through a long series of domains before the fake news content is served. Qurium found Doppelganger relies on a sophisticated “domain cloaking” service, a technology that allows websites to present different content to search engines compared to what regular visitors see. The use of cloaking services helps the disinformation sites remain online longer than they otherwise would, while ensuring that only the targeted audience gets to view the intended content.

Qurium discovered that Doppelganger’s cloaking service also promoted online dating sites, and shared much of the same infrastructure with VexTrio, which is thought to be the oldest malicious traffic distribution system (TDS) in existence. While TDSs are commonly used by legitimate advertising networks to manage traffic from disparate sources and to track who or what is behind each click, VexTrio’s TDS largely manages web traffic from victims of phishing, malware, and social engineering scams.

BREAKING BAD

Digging deeper, Qurium noticed Doppelganger’s cloaking service used an Internet provider in Switzerland as the first entry point in a chain of domain redirections. They also noticed the same infrastructure hosted a pair of co-branded affiliate marketing services that were driving traffic to sketchy adult dating sites: LosPollos[.]com and TacoLoco[.]co.

The LosPollos ad network incorporates many elements and references from the hit series “Breaking Bad,” mirroring the fictional “Los Pollos Hermanos” restaurant chain that served as a money laundering operation for a violent methamphetamine cartel.

Affiliates who sign up with LosPollos are given JavaScript-heavy “smartlinks” that drive traffic into the VexTrio TDS, which in turn distributes the traffic among a variety of advertising partners, including dating services, sweepstakes offers, bait-and-switch mobile apps, financial scams and malware download sites.

LosPollos affiliates typically stitch these smart links into WordPress websites that have been hacked via known vulnerabilities, and those affiliates will earn a small commission each time an Internet user referred by any of their hacked sites falls for one of these lures.

According to Qurium, TacoLoco is a traffic monetization network that uses deceptive tactics to trick Internet users into enabling “push notifications,” a cross-platform browser standard that allows websites to show pop-up messages which appear outside of the browser. For example, on Microsoft Windows systems these notifications typically show up in the bottom right corner of the screen — just above the system clock.

In the case of VexTrio and TacoLoco, the notification approval requests themselves are deceptive — disguised as “CAPTCHA” challenges designed to distinguish automated bot traffic from real visitors. For years, VexTrio and its partners have successfully tricked countless users into enabling these site notifications, which are then used to continuously pepper the victim’s device with a variety of phony virus alerts and misleading pop-up messages.

According to a December 2024 annual report from GoDaddy, nearly 40 percent of compromised websites in 2024 redirected visitors to VexTrio via LosPollos smartlinks.

ADSPRO AND TEKNOLOGY

On November 14, 2024, Qurium published research to support its findings that LosPollos and TacoLoco were services operated by Adspro Group, a company registered in the Czech Republic and Russia, and that Adspro runs its infrastructure at the Swiss hosting providers C41 and Teknology SA.

Qurium noted the LosPollos and TacoLoco sites state that their content is copyrighted by ByteCore AG and SkyForge Digital AG, both Swiss firms that are run by the owner of Teknology SA, Giulio Vitorrio Leonardo Cerutti. Further investigation revealed LosPollos and TacoLoco were apps developed by a company called Holacode, which lists Cerutti as its CEO.

The apps marketed by Holacode include numerous VPN services, as well as one called Spamshield that claims to stop unwanted push notifications. But in January, Infoblox said they tested the app on their own mobile devices, and found it hides the user’s notifications, and then after 24 hours stops hiding them and demands payment. Spamshield subsequently changed its developer name from Holacode to ApLabz, although Infoblox noted that the Terms of Service for several of the rebranded ApLabz apps still referenced Holacode in their terms of service.

Incredibly, Cerutti threatened to sue me for defamation before I’d even uttered his name or sent him a request for comment (Cerutti sent the unsolicited legal threat back in January after his company and my name were merely tagged in an Infoblox post on LinkedIn about VexTrio).

Asked to comment on the findings by Qurium and Infoblox, Cerutti vehemently denied being associated with VexTrio. Cerutti asserted that his companies all strictly adhere to the regulations of the countries in which they operate, and that they have been completely transparent about all of their operations.

“We are a group operating in the advertising and marketing space, with an affiliate network program,” Cerutti responded. “I am not [going] to say we are perfect, but I strongly declare we have no connection with VexTrio at all.”

“Unfortunately, as a big player in this space we also get to deal with plenty of publisher fraud, sketchy traffic, fake clicks, bots, hacked, listed and resold publisher accounts, etc, etc.,” Cerutti continued. “We bleed lots of money to such malpractices and conduct regular internal screenings and audits in a constant battle to remove bad traffic sources. It is also a highly competitive space, where some upstarts will often play dirty against more established mainstream players like us.”

Working with Qurium, researchers at the security firm Infoblox released details about VexTrio’s infrastructure to their industry partners. Just four days after Qurium published its findings, LosPollos announced it was suspending its push monetization service. Less than a month later, Adspro had rebranded to Aimed Global.

A REVEALING PIVOT

In March 2025, researchers at GoDaddy chronicled how DollyWay — a malware strain that has consistently redirected victims to VexTrio throughout its eight years of activity — suddenly stopped doing that on November 20, 2024. Virtually overnight, DollyWay and several other malware families that had previously used VexTrio began pushing their traffic through another TDS called Help TDS.

Digging further into historical DNS records and the unique code scripts used by the Help TDS, Infoblox determined it has long enjoyed an exclusive relationship with VexTrio (at least until LosPollos ended its push monetization service in November).

In a report released today, Infoblox said an exhaustive analysis of the JavaScript code, website lures, smartlinks and DNS patterns used by VexTrio and Help TDS linked them with at least four other TDS operators (not counting TacoLoco). Those four entities — Partners House, BroPush, RichAds and RexPush — are all Russia-based push monetization programs that pay affiliates to drive signups for a variety of schemes, but mostly online dating services.

“As Los Pollos push monetization ended, we’ve seen an increase in fake CAPTCHAs that drive user acceptance of push notifications, particularly from Partners House,” the Infoblox report reads. “The relationship of these commercial entities remains a mystery; while they are certainly long-time partners redirecting traffic to one another, and they all have a Russian nexus, there is no overt common ownership.”

Renee Burton, vice president of threat intelligence at Infoblox, said the security industry generally treats the deceptive methods used by VexTrio and other malicious TDSs as a kind of legally grey area that is mostly associated with less dangerous security threats, such as adware and scareware.

But Burton argues that this view is myopic, and helps perpetuate a dark adtech industry that also pushes plenty of straight-up malware, noting that hundreds of thousands of compromised websites around the world every year redirect victims to the tangled web of VexTrio and VexTrio-affiliate TDSs.

“These TDSs are a nefarious threat, because they’re the ones you can connect to the delivery of things like information stealers and scams that cost consumers billions of dollars a year,” Burton said. “From a larger strategic perspective, my takeaway is that Russian organized crime has control of malicious adtech, and these are just some of the many groups involved.”

WHAT CAN YOU DO?

As KrebsOnSecurity warned way back in 2020, it’s a good idea to be very sparing in approving notifications when browsing the Web. In many cases these notifications are benign, but as we’ve seen there are numerous dodgy firms that are paying site owners to install their notification scripts, and then reselling that communications pathway to scammers and online hucksters.

If you’d like to prevent sites from ever presenting notification requests, all of the major browser makers let you do this — either across the board or on a per-website basis. While it is true that blocking notifications entirely can break the functionality of some websites, doing this for any devices you manage on behalf of your less tech-savvy friends or family members might end up saving everyone a lot of headache down the road.

To modify site notification settings in Mozilla Firefox, navigate to Settings, Privacy & Security, Permissions, and click the “Settings” tab next to “Notifications.” That page will display any notifications already permitted and allow you to edit or delete any entries. Tick the box next to “Block new requests asking to allow notifications” to stop them altogether.

In Google Chrome, click the icon with the three dots to the right of the address bar, scroll all the way down to Settings, Privacy and Security, Site Settings, and Notifications. Select the “Don’t allow sites to send notifications” button if you want to banish notification requests forever.

In Apple’s Safari browser, go to Settings, Websites, and click on Notifications in the sidebar. Uncheck the option to “allow websites to ask for permission to send notifications” if you wish to turn off notification requests entirely.