Hackers Use Malware to Hijack Claude AI Accounts and Drain Subscriptions

The trouble began when security researchers and users noticed suspicious activity in Claude AI accounts. Attackers had found a way to steal active login sessions using infostealer malware. This type of malware infects a user's device and grabs the session tokens used by browsers to keep users logged in, allowing hackers to access accounts without needing passwords or triggering two-factor authentication.

Anthropic, the company behind Claude, quickly identified the threat. They traced the problem to malware families like Vidar and RedLine on Windows, as well as Atomic Stealer on macOS. With these tools, cybercriminals could hijack accounts and make unauthorized purchases using stored payment methods.

On August 31, Anthropic began warning users about the ongoing attacks and the risks of malware stealing active login sessions. They started signing out compromised accounts and removing payment methods to prevent further losses, as reported that day.

Affected users received notifications about the breach, and Anthropic initiated refunds for any unauthorized charges. Security experts confirmed that the malware could bypass standard security protocols, including two-factor authentication, because it used already-authenticated session tokens.

The situation escalated on September 1 when researchers discovered a fake desktop app called Claude Opus 5 circulating online. This app, which was not released by Anthropic, contained the RevStealer malware. Once installed, it could steal browser data, passwords, and even cryptocurrency wallet information from Windows users.

Further investigations revealed that the campaign behind the fake app was turning the popularity of Claude AI into a lure for more victims. The malware was distributed through a trojanized Electron application and a malicious GitHub repository. Security teams and Anthropic continued to alert users and take down fake sites.

Anthropic has locked out affected users, removed compromised payment information, and issued refunds for confirmed unauthorized transactions. The company is still investigating the full scope of the breach and encouraging users to check their devices for malware.

The attackers exploited a weakness in session management rather than a flaw in Claude itself, making device security the main concern. Anthropic and security experts are urging users to revoke active sessions, run malware scans, and be wary of third-party Claude apps or downloads.

It remains unclear how many users were affected and whether the attackers will attempt new strategies. Anthropic is likely to introduce further security measures, and users are being advised to stay alert for further phishing attempts or malware campaigns targeting AI platforms.