Hackers Steal Claude Usage Tokens from Subscribers

Summary

Independent AI consultant Grant De Swardt noticed his Claude Max 20x token usage rising even when he was not working and had paused scheduled tasks and cloud execution. Anthropic suspended his $200-per-month account, invalidated sessions and server-side Claude Code tokens, and refunded £44.49 for the unused subscription period. The company later said a compromised Claude session key had been used to mint unauthorized Claude Code OAuth tokens for activity apparently serving other people, although it could not determine how the access was obtained. De Swardt said Anthropic could not provide itemized usage records, leaving him unable to identify what consumed his allowance. Other users reported automatic upgrades, charges, and rapid or repeated depletion of their quotas without active use. In emails shared by some users, Anthropic attributed similar incidents to infostealer malware that steals login sessions from computers; it said it had signed affected users out, invalidated authorizations, issued some refunds, and warned that their devices might be infected. De Swardt found no evidence that his own computer was compromised, and his account was restored after about two weeks. Frustrated by the support process and the lack of usage visibility, he cancelled Claude for Cursor, which supports multiple models, including lower-cost open-source options. Anthropic declined to explain how users can identify misuse.