A malvertising campaign leveraging Bing search results has been observed distributing the SectopRAT malware through a deceptive Claude desktop application installer. The operation, dubbed "FakeAgent" by researchers at Huntress, compromised at least 29 organizations between July 21 and 22.
The attack chain began with malicious advertisements on Bing, which directed users to a legitimate Claude.ai domain. On this domain, a malicious "Claude Artifact" was hosted, which then redirected visitors to websites hosting a fake installer named "ClaudeDesktop.exe." This tactic of using a legitimate domain to host a malicious artifact was previously seen in early 2026, pushing macOS malware via "ClickFix" lures.
Huntress researchers reported that the malicious Claude Artifact was downloaded 7,100 times before Anthropic, the developer of Claude, removed it. The "ClaudeDesktop.exe" file itself is a legitimate JetBrains Chromium component. However, it is used to sideload a malicious DLL, "libcef.dll," which then delivers the SectopRAT remote access trojan.
Persistence on compromised systems is achieved through another executable, "DockerDesktop.exe," which installs a scheduled task. The various loaders and staging components in the infection chain incorporate anti-analysis mechanisms, including VMProtect packing, shader timing checks, GPU and VRAM checks, and virtual machine detection.
SectopRAT, also known as ArechClient2, has been active since 2019 and is an information-stealing remote access trojan with Hidden Virtual Network Computing (HVNC) functionality. This allows for remote hands-on operations and real-time interaction with compromised systems. The malware targets a wide range of sensitive data, including user passwords, credit card information, files, browser logins and cookies, FTP credentials, and data from messaging clients like Discord and Telegram, as well as Steam and various VPN products.
The malware utilizes the EtherHiding technique to retrieve its command-and-control (C2) address by monitoring Ethereum BNB Smart Chain transactions. SectopRAT has previously been distributed through "CastleLoader" campaigns and "ClickFix" attacks.
In an unusual turn, Huntress researchers reported using Claude Opus 4.8 to assist with their analysis, specifically for shader emulation, cryptographic reconstruction, and .NET code analysis. This aid helped in decrypting the .NET payload, confirming it as SectopRAT or a closely related variant, and facilitating infrastructure analysis.
Through this analysis, researchers identified 10 domains registered to the same email address since December 2025. One of these domains had previously been linked to StealC malware distribution and was seized during "Operation Endgame." Despite these findings, Huntress stated they lack sufficient evidence to attribute the FakeAgent campaign to a specific, known threat cluster.
Users are advised to download software exclusively from official websites and trusted download portals, rather than relying on search results, especially sponsored advertisements, to mitigate risks from such malvertising campaigns.
