Ryuk Ransomware Targeting Major Companies | Expert Analysis
Discover how Ryuk ransomware targets major companies with AI-powered tools to detect unusual activity. Learn the threats behind Autonomous Response technology.
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Written by
Max Heinemeyer
Global Field CISO
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Oct 2019
In recent years, cyber-criminals have increasingly directed their efforts toward sophisticated, long-haul attacks against major companies — a tactic known as “big game hunting.” Unlike standardized phishing campaigns that aim to deliver malware en masse, big game hunting involves exploiting the particular vulnerabilities of a single, high-value target. Catching such attacks requires AI-powered tools that learn what’s normal for each unique user and device, thereby shining a light on the subtle signs of unusual activity that they introduce.
In the threat detailed below, cyber-criminals targeted a major firm with Ryuk ransomware, which Darktrace observed during a trial deployment period. Leveraged very often in the final stage of such tailored attacks, Ryuk encrypts only crucial assets in each targeted environment that the attackers have handpicked. Here’s how this particular incident unfolded, as well as how AI Autonomous Response technology, if in active mode, would have contained the threat in seconds:
Incident overview
Figure 1: Clustering of alerts during intrusion (top right)
Rooted in its evolving understanding of ‘self’ for the targeted firm, Darktrace AI flagged myriad instances of anomalous behavior over the course of the incident — each represented by a dot in the visualization above. The anomalous activity is organized vertically according to how unusual each behavior was in comparison to “normal” for the users and devices involved. The colored dots represent particularly high-confidence detections, which should have prompted immediate investigation by the security team.
Compromised admin keys
The first sign of attack was the highly unusual use of an administrator account not previously seen on the network, suggesting that the attackers had gained access to the account outside the limited scope of the Darktrace trial before moving laterally to the monitored environments. Had Darktrace been deployed across the digital infrastructure, the initial hijacking of the account would have been obvious right away. Nevertheless, Darktrace alerted on the anomalous admin session repeatedly and in real time, as shown below:
Figure 2: Strong detections of compromised admin credential
This behavior is typical of big game hunting. Rather than firing their payload straight away upon accessing the network, the attackers engaged in a longer-term compromise to attain the best position for a crippling attack.
Infiltration via TrickBot
Darktrace then detected the infamous TrickBot banking trojan being downloaded onto the network. While the attacker already had access via the compromised admin credentials, Trickbot was used as a loader for further malicious files and as an additional command & control (C&C) channel. Among the most common post-exploitation steps were:
Figure 3: Detection of later-stage Trickbot download
Command & Control communication
Once the Trickbot infection had begun, Darktrace observed C&C communication back to the attackers. And whereas many devices exhibited anomalous behavior, Darktrace pinpointed one such device at the nexus of the infection. The below image illustrates the plethora of suspicious connections detected on this single device:
Figure 4: Every coloured dot represents a Darktrace detection — very obvious chains of malicious activity is seen above
Using TLS Fingerprinting — also called JA3, the subject of a previous blog post — Darktrace detected a new piece of software making encrypted connections from this device to multiple unusual destinations, a behavior known as beaconing.
Figure 5: The communication in this graph is filtered down to unusual TLS connections — clearly showing a spike in communication during the compromise
Ransomware encryption commences
Following the establishment of the connection with the C&C infrastructure, the Ryuk ransomware was finally deployed. During this “noisy” period with many suspicious SMB activities, Darktrace even more clearly indicated the seriousness and extent of the attack:
Figure 6: A sample of different, non-signature dependant Ransomware detections that fired
In just 12 hours, Ryuk had encrypted more than 200,000 files. The entire incident took place over 36 hours — after that, the company shut down its network to prevent further damage.
Ransomware retrospective
Following the incident, the business traced the initial compromise back to a part of their network in another country that Darktrace did not have visibility over during this trial period. The infection spread until it reached a recently installed file server that Darktrace was, in fact, monitoring. The attacker likely got access to an administrative account that had been used to build this server and, at that point, they had the access needed to fire the Ryuk ransomware.
This incident put Darktrace in the unique position of observing a ransomware attack wherein none of the alerts were seen or actioned by the internal IT team, demonstrating what such an attack can do absent any intervention and response. Had the company actively monitored its Darktrace deployment, the security team would have received and actioned the alerts in real time, as its thousands of users do on a daily basis.
Autonomous Response to the rescue
Had the firm deployed Autonomous Response technology, the lack of attention afforded to Darktrace’s alerts would not have mattered. Whereas four hours passed from the executable download to the first encrypted file, Autonomous Response would have neutralized the threat within seconds, preventing widespread damage and giving the security team the crucial time to catch up.
The screenshot below shows an excerpt of Darktrace’s detections at the beginning of the file server compromise. The detections are listed in chronological order from bottom to top, along with the action that Darktrace’s AI Autonomous Response tool, Antigena, would have taken:
In sum, Antigena would have taken appropriate action by enforcing normal behavior, rather than applying a binary block (e.g. completely quarantining the device) as legacy tools would.
Darktrace cyber analysts are world-class experts in threat intelligence, threat hunting and incident response, and provide 24/7 SOC support to thousands of Darktrace customers around the globe. Inside the SOC is exclusively authored by these experts, providing analysis of cyber incidents and threat trends, based on real-world experience in the field.
Atomic Stealer: Darktrace’s Investigation of a Growing macOS Threat
The Rise of Infostealers Targeting Apple Users
In a threat landscape historically dominated by Windows-based threats, the growing prevalence of macOS information stealers targeting Apple users is becoming an increasing concern for organizations. Infostealers are a type of malware designed to steal sensitive data from target devices, often enabling attackers to extract credentials and financial data for resale or further exploitation. Recent research identified infostealers as the largest category of new macOS malware, with an alarming 101% increase in the last two quarters of 2024 [1].
What is Atomic Stealer?
Among the most notorious is Atomic macOS Stealer (or AMOS), first observed in 2023. Known for its sophisticated build, Atomic Stealer can exfiltrate a wide range of sensitive information including keychain passwords, cookies, browser data and cryptocurrency wallets.
Originally marketed on Telegram as a Malware-as-a-Service (MaaS), Atomic Stealer has become a popular malware due to its ability to target macOS. Like other MaaS offerings, it includes services like a web panel for managing victims, with reports indicating a monthly subscription cost between $1,000 and $3,000 [2]. Although Atomic Stealer’s original intent was as a standalone MaaS product, its unique capability to target macOS has led to new variants emerging at an unprecedented rate
Even more concerning, the most recent variant has now added a backdoor for persistent access [3]. This backdoor presents a significant threat, as Atomic Stealer campaigns are believed to have reached an around 120 countries. The addition of a backdoor elevates Atomic Stealer to the rare category of backdoor deployments potentially at a global scale, something only previously attributed to nation-state threat actors [4].
This level of sophistication is also evident in the wide range of distribution methods observed since its first appearance; including fake application installers, malvertising and terminal command execution via the ClickFix technique. The ClickFix technique is particularly noteworthy: once the malware is downloaded onto the device, users are presented with what appears to be a legitimate macOS installation prompt. In reality, however, the user unknowingly initiates the execution of the Atomic Stealer malware.
This blog will focus on activity observed across multiple Darktrace customer environments where Atomic Stealer was detected, along with several indicators of compromise (IoCs). These included devices that successfully connected to endpoints associated with Atomic Stealer, those that attempted but failed to establish connections, and instances suggesting potential data exfiltration activity.
Darktrace’s Coverage of Atomic Stealer
As this evolving threat began to spread across the internet in June 2025, Darktrace observed a surge in Atomic Stealer activity, impacting numerous customers in 24 different countries worldwide. Initially, most of the cases detected in 2025 affected Darktrace customers within the Europe, Middle East, and Africa (EMEA) region. However, later in the year, Darktrace began to observe a more even distribution of cases across EMEA, the Americas (AMS), and Asia Pacific (APAC). While multiple sectors were impacted by Atomic Stealer, Darktrace customers in the education sector were the most affected, particularly during September and October, coinciding with the return to school and universities after summer closures. This spike likely reflects increased device usage as students returned and reconnected potentially compromised devices to school and campus environments.
Starting from June, Darktrace detected multiple events of suspicious HTTP activity to external connections to IPs in the range 45.94.47.0/24. Investigation by Darktrace’s Threat Research team revealed several distinct patterns ; HTTP POST requests to the URI “/contact”, identical cURL User Agents and HTTP requests to “/api/tasks/[base64 string]” URIs.
Within one observed customer’s environment in July, Darktrace detected two devices making repeated initiated HTTP connections over port 80 to IPs within the same range. The first, Device A, was observed making GET requests to the IP 45.94.47[.]158 (AS60781 LeaseWeb Netherlands B.V.), targeting the URI “/api/tasks/[base64string]” using the “curl/8.7.2” user agent. This pattern suggested beaconing activity and triggered the ‘Beaconing Activity to External Rare' model alert in Darktrace / NETWORK, with Device A’s Model Event Log showing repeated connections. The IP associated with this endpoint has since been flagged by multiple open-source intelligence (OSINT) vendors as being associated with Atomic Stealer [5].
Figure 1: Darktrace’s detection of Device A showing repeated connections to the suspicious IP address over port 80, indicative of beaconing behavior.
Darktrace’s Cyber AI Analyst subsequently launched an investigation into the activity, uncovering that the GET requests resulted in a ‘503 Service Unavailable’ response, likely indicating that the server was temporarily unable to process the requests.
Figure 2: Cyber AI Analyst Incident showing the 503 Status Code, indicating that the server was temporarily unavailable.
This unusual activity prompted Darktrace’s Autonomous Response capability to recommend several blocking actions for the device in an attempt to stop the malicious activity. However, as the customer’s Autonomous Response configuration was set to Human Confirmation Mode, Darktrace was unable to automatically apply these actions. Had Autonomous Response been fully enabled, these connections would have been blocked, likely rendering the malware ineffective at reaching its malicious command-and-control (C2) infrastructure.
Figure 3: Autonomous Response’s suggested actions to block suspicious connectivity on Device A in the first customer environment.
In another customer environment in August, Darktrace detected similar IoCs, noting a device establishing a connection to the external endpoint 45.94.47[.]149 (ASN: AS57043 Hostkey B.V.). Shortly after the initial connections, the device was observed making repeated requests to the same destination IP, targeting the URI /api/tasks/[base64string] with the user agent curl/8.7.1, again suggesting beaconing activity. Further analysis of this endpoint after the fact revealed links to Atomic Stealer in OSINT reporting [6].
Figure 4: Cyber AI Analyst investigation finding a suspicious URI and user agent for the offending device within the second customer environment.
As with the customer in the first case, had Darktrace’s Autonomous Response been properly configured on the customer’s network, it would have been able to block connectivity with 45.94.47[.]149. Instead, Darktrace suggested recommended actions that the customer’s security team could manually apply to help contain the attack.
Figure 5: Autonomous Response’s suggested actions to block suspicious connectivity to IP 45.94.47[.]149 for the device within the second customer environment.
In the most recent case observed by Darktrace in October, multiple instances of Atomic Stealer activity were seen across one customer’s environment, with two devices communicating with Atomic Stealer C2 infrastructure. During this incident, one device was observed making an HTTP GET request to the IP 45.94.47[.]149 (ASN: AS60781 LeaseWeb Netherlands B.V.). These connections targeted the URI /api/tasks/[base64string, using the user agent curl/8.7.1.
Shortly afterward, the device began making repeated connections over port 80 to the same external IP, 45.94.47[.]149. This activity continued for several days until Darktrace detected the device making an HTTP POST request to a new IP, 45.94.47[.]211 (ASN: AS57043 Hostkey B.V.), this time targeting the URI /contact, again using the curl/8.7.1 user agent. Similar to the other IPs observed in beaconing activity, OSINT reporting later linked this one to information stealer C2 infrastructure [7].
Figure 6: Darktrace’s detection of suspicious beaconing connectivity with the suspicious IP 45.94.47.211.
Further investigation into this customer’s network revealed that similar activity had been occurring as far back as August, when Darktrace detected data exfiltration on a second device. Cyber AI Analyst identified this device making a single HTTP POST connection to the external IP 45.94.47[.]144, another IP with malicious links [8], using the user agent curl/8.7.1 and targeting the URI /contact.
Figure 7: Cyber AI Analyst investigation finding a successful POST request to 45.94.47[.]144 for the device within the third customer environment.
A deeper investigation into the technical details within the POST request revealed the presence of a file named “out.zip”, suggesting potential data exfiltration.
Figure 8: Advanced Search log in Darktrace / NETWORK showing “out.zip”, indicating potential data exfiltration for a device within the third customer environment.
Similarly, in another environment, Darktrace was able to collect a packet capture (PCAP) of suspected Atomic Stealer activity, which revealed potential indicators of data exfiltration. This included the presence of the “out.zip” file being exfiltrated via an HTTP POST request, along with data that appeared to contain details of an Electrum cryptocurrency wallet and possible passwords.
Read more about Darktrace’s full deep dive into a similar case where this tactic was leveraged by malware as part of an elaborate cryptocurrency scam.
Figure 9: PCAP of an HTTP POST request showing the file “out.zip” and details of Electrum Cryptocurrency wallet.
Although recent research attributes the “out.zip” file to a new variant named SHAMOS [9], it has also been linked more broadly to Atomic Stealer [10]. Indeed, this is not the first instance where Darktrace has seen the “out.zip” file in cases involving Atomic Stealer either. In a previous blog detailing a social engineering campaign that targeted cryptocurrency users with the Realst Stealer, the macOS version of Realst contained a binary that was found to be Atomic Stealer, and similar IoCs were identified, including artifacts of data exfiltration such as the “out.zip” file.
Conclusion
The rapid rise of Atomic Stealer and its ability to target macOS marks a significant shift in the threat landscape and should serve as a clear warning to Apple users who were traditionally perceived as more secure in a malware ecosystem historically dominated by Windows-based threats.
Atomic Stealer’s growing popularity is now challenging that perception, expanding its reach and accessibility to a broader range of victims. Even more concerning is the emergence of a variant embedded with a backdoor, which is likely to increase its appeal among a diverse range of threat actors. Darktrace’s ability to adapt and detect new tactics and IoCs in real time delivers the proactive defense organizations need to protect themselves against emerging threats before they can gain momentum.
Credit to Isabel Evans (Cyber Analyst), Dylan Hinz (Associate Principal Cyber Analyst) Edited by Ryan Traill (Analyst Content Lead)
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With a proven approach that gets results. Darktrace’s unique business-centric anomaly detection catches advanced phishing, supply chain compromises, and BEC attacks – detecting them on average 13 days earlier than attack-centric solutions. That’s why 75% of our customers have removed their SEG and now rely on their native email security provider combined with Darktrace.
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![Autonomous Response’s suggested actions to block suspicious connectivity to IP 45.94.47[.]149 for the device within the second customer environment.](https://cdn.prod.website-files.com/626ff4d25aca2edf4325ff97/6931e3cb1ddc36af8205720b_Screenshot%202025-12-04%20at%2011.40.54%E2%80%AFAM.png)
![Cyber AI Analyst investigation finding a successful POST request to 45.94.47[.]144 for the device within the third customer environment.](https://cdn.prod.website-files.com/626ff4d25aca2edf4325ff97/6931e41d22eb7e9a3e8217d5_Screenshot%202025-12-04%20at%2011.42.15%E2%80%AFAM.png)
