Dateline: September 1, 2026
There is no free desktop version of Claude Opus 5. But a GitHub page is betting you don’t know that.
Security researchers found a fake “Claude Opus 5 Free Desktop” app that promises free access to a paid AI model. Instead of an AI tool, it drops a Windows password stealer called RevStealer onto your machine. The malware grabs your saved logins, browser data, and crypto wallets, then deletes itself so almost nothing is left to find.
What Happened
A GitHub repository was set up to look like an official Anthropic release. It offered a download called ClaudeOpus5-desktop.zip, sized at around 101 MB, with screenshots and model comparison charts to look real. The same malware also showed up on game cheat websites, so the lure changes but the payload stays the same.
Run the file and nothing opens. No window. No AI app. Behind the scenes, a hidden Electron program acts as a loader. Before it does anything, it checks whether it is running on a real person’s computer. It looks at memory, processor count, hostname, username, and graphics hardware. It runs a batch of checks to spot virtual machines and malware sandboxes. If the machine looks like a research setup, the malware waits a few seconds and quits. It also shuts down on systems set to Russian, Ukrainian, and several Central Asian languages.
If the machine passes those checks, it tries to hide its folder from Microsoft Defender, unpacks an encrypted payload into a random AppData folder, and starts stealing.
What’s the Impact
RevStealer is built for a fast, quiet theft. It goes after browser databases, cookies, and saved passwords. It pulls records from more than a dozen password managers. It targets more than 50 cryptocurrency wallets. It also grabs VPN and remote access credentials, messaging app data, game launcher accounts, clipboard contents, screenshots, and selected documents.
The stolen data does not sit on your disk in one big file. It streams out in small encrypted pieces to a server the attacker controls, which makes it harder for security tools to catch. For Chrome and Edge, it even launches the browser under debugger control to grab newer encryption keys straight from memory.
Two things make cleanup harder. First, the malware self deletes after it runs, so there are few traces left to investigate. Second, if the attacker’s main server goes down, the malware pulls a backup address from a smart contract on the Polygon blockchain. That lets the operators switch infrastructure without rebuilding anything, so a simple server takedown does not stop them.
One person on a public forum described their Microsoft and EA accounts being compromised soon after running the download. At the time it was checked, only one of 66 antivirus engines flagged the file.
One run. Everything worth stealing.
RevStealer does not go after one thing. Once it clears its checks, it sweeps six categories of data in a single short session, then streams it all out in small encrypted pieces.
The data never sits on your disk as one big file. It leaves in small encrypted pieces, which makes the theft much harder to catch in the act.
How to Avoid This
Treat “free” versions of paid AI tools as a red flag. That is the whole trick here.
- Download AI apps only from the vendor’s official website, not GitHub mirrors, release pages, or gaming forums.
- Block program execution from user-writable folders like AppData and Downloads where you can.
- Watch for unusual access to browser credential stores and wallet files. That behavior is the real signal, since file hashes change constantly.
- If you suspect infection, move fast. Revoke active sessions, reset passwords, and move any crypto funds before the attacker does.
- Review browser extensions regularly, since session and wallet theft often rides on the same access.
This is the same pattern we broke down when compromised browser extensions and weak password manager storage exposed saved credentials. Trusted brands and trusted file formats keep getting used as cover, the way attackers abused PDF files and cloud trust to steal Dropbox logins.