Anthropic Claude Users Targeted in Multi-Platform Infostealer Campaign
In August 2026, Anthropic detected unauthorized access to Claude AI accounts after threat actors used multiple infostealer malware variants including Vidar, Lumma, StealC, RedLine, Acreed, and Atomic Stealer to harvest user session cookies and authentication tokens. The attackers bypassed multifactor authentication by stealing active browser sessions rather than credentials, allowing them to consume users' Claude usage quotas and access saved payment information. Anthropic responded by forcibly signing out affected users, removing payment methods, and refunding unauthorized charges. This incident exemplifies the growing shift from credential-based attacks to session hijacking, as organizations strengthen password policies and MFA adoption. The attack highlights emerging threats against AI platforms and the need for enhanced session management controls in cloud-native applications.
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