WhatsApp Worm Infects Devices and Compromises User Banking Information
There has been a troubling revelation in the cybersecurity community that cybercriminals continue to weaponise trusted digital ecosystems by deploying highly sophisticated malware campaigns that use WhatsApp's messaging platform to infiltrate users throughout Brazil, demonstrating that cybercriminals continue to use trusted digital ecosystems to their advantage.
This large-scale operation, which was detected on September 29, 2025, exhibits unprecedented technical precision and social engineering skills, manipulating user trust in order to achieve rapid and silent propagation of the virus.
There has been an increased use of WhatsApp Web by the attackers in attempts to propagate malicious LNK and ZIP files disguised as harmless attachments sent from compromised contacts.
The attackers have chosen to send misleading messages that convincingly mimic genuine communication to lure their victims into execution.
The moment that an unsuspecting recipient opens a file that contains malware on a desktop system, the malware stealthily executes a fileless infection chain, which is designed to steal credentials from financial institutions as well as cryptocurrency exchanges as they conduct their transactions.
Researchers have determined that the campaign was linked to a broader operation known as "Water Saci," which shows a level of sophistication and scale not typically seen in regional cybercrime. There is evidence in the code of the malware, Maverick and Sorvepotel, that is code-like to the notorious Coyote Trojan, pointing to a new evolution of Brazilian cybercrime tools that target the thriving ecosystem of digital finance in the country.
In contrast to typical attacks that are primarily focused on data theft and ransomware deployment, this particular operation places a high value on rapid self-propagation and wide infiltration.
By cleverly leveraging social relationships, the infection process distributes malicious files through the accounts of already infected users to embed itself deeper into trusted networks as a result.
It is estimated that over 400 corporate environments have already been compromised by this threat, and more than 1,000 endpoints have been affected, proving that the campaign's aggressive reach and operational efficiency are evident because command-and-control servers validate each download to ensure that it comes directly from the malware.
Nevertheless, this technique complicates automated security analysis and network defence, making it significantly more difficult to detect and deter the threat.
The malware was written primarily in Portuguese and distributed by localised URLs. As a result of its design, it suggests that a deliberate effort was made to target the individual consumer as well as corporate users in Brazil's rapidly growing cryptocurrency and financial sectors.
Besides the campaign's regional implications, this campaign serves as a stark reminder of the convergence that has been taking place in modern cyberattacks between social manipulation and advanced technical execution.
With this new wave of WhatsApp-targeted malware exploiting trust, automation, and the interconnectedness of messaging platforms, people are witnessing a concerning shift in the cyber threat landscape, one where they can no longer assume the familiar is safe. It has been reported that the Sorvepotel malware has impacted many sectors throughout Brazil, not just individual users. The malware has penetrated a wide range of sectors throughout the country.
A Trend Micro cybersecurity researcher stated that public and government service organisations have been the most severely affected, followed by manufacturing, technology, education, and construction organisations. However, as attackers continue to refine and expand their tactics, other Latin American countries may soon have to face similar threats.
Although the current campaign is focusing primarily on Brazil, experts warn that similar threats may soon impact other Latin American countries.
There is no doubt that the Sovepotel infection chain is extremely deceptive. It spreads mainly through phishing messages sent via compromised contacts' WhatsApp accounts. It is common for these messages, which appear to come from trusted friends or colleagues, to contain malicious ZIP files, which appear as if they were legitimate files-such as receipts, budget documents, or health-related documents, written in Portuguese.
These files are aimed at attracting enterprise users rather than casual mobile users, as they are urged to open them on desktop computers. Once the malware has been executed, it will spread automatically through WhatsApp Web, sending mass messages which will not only expedite its spread but will also lead to the suspension of infected accounts for excessive spam activity, as well as the spreading of the malware.
Several researchers have noticed that, in addition to parallel phishing campaigns through email, attackers may also distribute ZIP files containing similar content from seemingly legitimate corporate addresses, increasing the likelihood of infection. There is already a substantial scale of operation, with over 400 customer environments reported as compromised, which is an indication that the worm has spread rapidly and is extremely effective in its operational aspects.
By targeting Brazilian financial institutions and cryptocurrency exchanges, the group illustrates a deliberate effort to monetise itself by stealing credentials and gaining unauthorised access to financial resources, even though analysts warn that the same techniques can be adapted to other countries as well.
Depending on the severity of the attack, financial consequences can range from immediate unauthorised withdrawals to long-term identity theft and the loss of a victim's reputation.
Cybersecurity experts, for this reason, emphasise the need to adopt multilayered defence strategies.
Educating users and organisations on how to keep them safe requires them to avoid suspicious links, even those shared by familiar contacts, as well as verify their authenticity by using alternative channels for communications. It is crucial to maintain an updated application base, enable two-factor authentication across financial and communication platforms, and keep reputable antivirus software in place to minimise exposure.
Additionally, it is important to monitor financial accounts for unusual activity and conduct frequent data backups to prevent future losses. It is important to note that research indicates that awareness and education remain the best defences, as they ensure both individuals and organisations are prepared to recognise, resist, and report emerging social engineering threats as soon as they emerge, so they are not caught by surprise.
Based on the technical analysis of the campaign, people have discovered that the infection mechanism in the campaign was highly sophisticated and stealthy in order to evade detection and achieve persistence without leaving any traditional forensic evidence. During the first stage of infection, a victim receives a malicious ZIP archive through WhatsApp Web, which contains a malicious LNK file disguised as a legitimate document.
These LNK files are often presented by generic names, or they are branded to resemble correspondence from a bank.
In the accompanying Portuguese language message, the recipient is advised to open the file on a computer, as it specifies that "visualisations can be performed only on computers," and even suggests Chrome users select the "keep file" option due to the ZIP format of the file.
When the LNK file has been executed, it launches cmd.exe with embedded commands that trigger a PowerShell script, which is responsible for contacting a remote command and control server via a PowerShell script.
Using this server, each request is meticulously verified, allowing downloads only if the "User-Agent" header is detected to be unique to the PowerShell process.
By doing so, the server effectively blocks unauthorised access and automated analysis attempts, blocking common attacks.
Using PowerShell, the embedded .NET file will be decoded and executed as a live assembly by using byte-level manipulation, thereby making the infection completely fileless, because it will be performed entirely in memory.
It is quite hard to reverse engineer this initial loader because it is heavily obfuscated by controlling flow flattening, indirect function calls, and randomised naming conventions.
A key part of the malware's function is to download and decrypt two encrypted shellcodes from the C2 server, authenticated by a cryptographic HMAC signature.
The attacker's custom key — "MaverickZapBot2025SecretKey12345"— generates an API token that allows it to fetch these payloads only. Additionally, the campaign is further protected from external scrutiny by the custom key.
The decrypted data contains a Doughnut-based loader that is responsible for initiating two distinct execution paths: the first delivers the “MaverickBanker” Trojan, while the second targets the WhatsApp infector module. Subsequent stages continue along this elaborate path.
Secondary loaders are responsible for retrieving a .NET assembly named "Maverick.StageOne," a component that will download and execute the WhatsApp infector, a self-propagating component intended to hijack a victim's session and automate the delivery of messages, in an attempt to hijack their data.
By using open-source automation tools like WPPConnect and Selenium browser drivers, this module can detect an active WhatsApp Web window and begin sending malicious files to the victim's contacts in order to maintain infection.
During this stage in Brazilian culture, WhatsApp is referred to as the “ZAP,” a colloquial term referring to its localised development and social engineering techniques.
Despite the multiple layers of obfuscation used in the malware, analysts have been able to reconstruct the malware's workflow, confirming that the malware has a modular structure, reuses shared functions, and intends to maintain a large-scale self-replication network across multiple interconnected networks, confirming its intent to be able to replicate itself.
With an intricate combination of automation, encryption, and behavioural evasion, large-scale cybercrime operations are being carried out using everyday communication tools in a manner that represents a new frontier in weaponising these tools. A technical analysis of the Water Saci campaign has demonstrated that an advanced and meticulously engineered infrastructure was used to ensure persistence, propagation, and stealth of the campaign.
During the first stage of the PowerShell script, an Explorer process is secretly launched, which will be used to retrieve further payloads from multiple command-and-control (C2) servers, including the ones hosting zapgrande.com, expansiveuser.com, and sorvetenopote.com.
As can be seen from embedded Portuguese-language comments embedded within the code, the threat actor intentionally attempted to weaken the system’s defences by executing commands in Microsoft Defender to disable User Account Control (UAC).
As a result of the deliberate security modifications, the malware can perform privileged operations uninterrupted, creating an environment where subsequent payloads are not detected.
In addition, the campaign delivers one of two distinct payloads, depending on the system profile of the victim: a legitimate Selenium browser automation framework, which is coupled with ChromeDriver, or the more destructive Maverick banking Trojan.
A Selenium component is used to simulate active browser sessions, enabling attackers to hijack WhatsApp Web accounts for the purpose of distributing malicious files to new victims, leading to the propagation of the worm's self-propagation cycle.
Maverick, on the other hand, focuses on credential theft, monitoring user browsing activity to determine how to gain access to Brazilian financial institutions and cryptocurrency exchanges before deploying additional. NET-based malwaretoo harvest sensitive information about their customers.
Despite the fact that the campaign is quite adaptable to the dual payload mechanism, the researchers from Trend Micro point out that, combined with the campaign's ability to spread independently, this represents a significant escalation in regional cyber threats, and if left unchecked, can easily spread beyond Latin America.
It is particularly challenging due to the campaign's worm-like nature: after the initial infection, the malware sends further malicious messages to the victim's WhatsApp contacts, creating a fast and exponential infection network based on the social trust that has been established. Because recipients are much more likely to open attachments from familiar sources, this strategy has a dramatic impact on the success rate of the malware.
In an effort to make the world a more secure place, cybercriminals are increasingly exploiting widely used communication platforms to deliver fileless and evasive attacks, according to experts, which marks a significant change in the global threat landscape. WhatsApp is used extensively across Brazil for personal and professional purposes and is therefore a lucrative target for cybercriminals.
Despite the growing threat, researchers have urged organisations to take proactive defensive measures to reduce risks.
It is recommended that administrators disable auto-downloads of media and documents on WhatsApp, implement firewall and endpoint policies restricting file transfers from personal applications, and enforce application whitelisting or containerization in BYOD environments to prevent malicious attacks.
The importance of employee awareness programs cannot be overstated - users need to be trained in recognising and reporting suspicious attachments and links, even those sent by trusted contacts. Responding quickly to PowerShell execution alerts as well as maintaining updated endpoint security tools can help further contain infections in their earliest stages.
Experts warn that to be able to fight these kinds of threats, companies must maintain vigilance, implement layers of defences, and foster an organisational culture that fosters awareness -- elements that have become increasingly important as malicious software that thrives on trust and connectivity spreads.
WhatsApp's "Water Saci" operation illustrates how cyber tactics are rapidly transforming the way people manage digital risk in everyday communication due to their rapid advancement. The attackers continue to exploit the familiarity of trusted platforms, so the user and organisation alike must adopt a more comprehensive protective framework that combines technology, awareness, and behavioural caution to protect themselves.
By implementing robust defences such as endpoint monitoring, adaptive threat detection, and strict file transfer controls, it may be possible to reduce exposure to such fileless and socially engineered threats. The reduction of infection rates can also be drastically reduced when the workplace culture is rooted in cybersecurity mindfulness-where verification precedes action.
The strategic collaboration between cybersecurity companies, financial institutions, and policy regulators will be crucial if people are to identify early signs of compromise and neutralise threats before they become a problem. It is important that individuals as well as organisations embed proactive vigilance and shared accountability as part of their digital habits, ensuring that trust in modern communication tools remains a strength instead of a weakness for both parties.
