Cybercriminals have launched a sophisticated malvertising campaign using a fake Claude‑AI website that installs a new Windows backdoor called “Beagle,” highlighting how attackers are weaponizing the popularity of AI tools against software developers. The deceptive site, reachable through sponsored search results, mimics Anthropic’s legitimate Claude interface and lures users into downloading what appears to be a productivity‑oriented “Claude‑Pro Relay” tool but is in fact a poisoned installer.
Modus operandi
The malicious domain claude‑pro[.]com presents a stripped‑down clone of the official Claude design, using similar colors and fonts to create a veneer of legitimacy. However, most navigation links on the page simply redirect back to the homepage, and the only functional element is a large download button that serves a 505‑MB archive named Claude‑Pro‑windows‑x64.zip, which contains a trojanized MSI installer. Users who bypass standard security hygiene—such as verifying the URL or ignoring suspicious “sponsored” tags—end up deploying this bundle on their machines.
Once the MSI executes, it drops three files into the Windows Startup folder: NOVupdate.exe, NOVupdate.exe.dat, and a malicious DLL named avk.dll. The first file is a legitimate, digitally signed updater from G Data security software, which attackers abuse via DLL sideloading to load the malicious avk.dll instead of the genuine library. This DLL decrypts the encrypted data file, then executes the open‑source in‑memory loader DonutLoader, which in turn deploys the final payload—the Beagle backdoor—entirely in memory to evade disk‑based detection.
Beagle backdoor capabilities
Beagle is a lightweight but dangerous Windows backdoor that gives attackers remote control over an infected system. It supports a small set of commands such as running arbitrary shell commands, uploading and downloading files, creating and renaming directories, listing folder contents, and uninstalling itself to destroy evidence. The malware communicates with its command‑and‑control server at license[.]claude‑pro[.]com over TCP port 443 or UDP port 8080, encrypting traffic with a hardcoded AES key to make network monitoring more difficult.
Attribution and broader implications
Security researchers have not yet pinned the campaign to a specific named threat group, but they note technical overlaps and suggest the same actors behind the PlugX malware family may be experimenting with this new payload. The fact that the attackers impersonate major security vendors in other related samples—such as Trellix, CrowdStrike, SentinelOne, and Microsoft Defender—points to a broader malvertising and supply‑chain‑style strategy.
How users and organizations can protect themselves
Organizations should block the domains claude‑pro[.]com and license[.]claude‑pro[.]com at the DNS and firewall level and search endpoints for NOVupdate.exe and avk.dll in Startup folders, which are strong indicators of compromise. End users, especially developers, must download Claude and similar AI tools only from verified official domains, treat sponsored search results with skepticism, and verify URLs before clicking installers. Updated endpoint protection, EDR logging, and user‑awareness training on AI‑related phishing and malvertising are critical to mitigating this evolving threat.