Infostealers can steal active Claude sessions, bypass 2FA and drain paid usage. Anthropic is revoking access and refunding unauthorized charges.Anthropic confirmed that several infostealer malware can hijack an active Claude login session and let attackers burn through your usage without ever touching your password.“Our investigation is ongoing. Our findings to date suggest that a computer you use with Claude is likely infected with infostealer malware, and may have been for some time. Phones and tablets do not appear to have been involved.” reads the notification sent to the impacted users.“We have no reason to believe that this malware is related to Claude, installed through Claude, or related to anything you did with Claude. It’s general-purpose malware that typically arrives with an unofficial download or a malicious app, and it quietly copies saved passwords, login cookies in browsers, and credentials for other apps running locally. Your Claude session was likely one of the many things it collected. It appears that a bad actor has now started picking the Claude sessions out of what it collected and using them.”Recently, Anthropic started signing some Claude users out and removing their saved payment cards. The reason? Infostealer malware on their computers stole active Claude sessions and gave attackers access to their accounts. “We recently signed you out of Claude and removed the payment method saved on your account, so you’ll need to log back in and re-add your card.” continues the report. “We’re sorry for the disruption. Here’s what happened and what we’ve done about it.”Anthropic detected the suspicious activity and identified multiple infostealer families affecting Windows and macOS. Infostealers bypass the login process by stealing authenticated browser sessions, allowing attackers to evade passwords, MFA and SSO and access paid Claude accounts. Revoking sessions or blocking fraudulent payments is not enough: if the malware remains on the device, it can capture the user’s next login and give attackers access again.Anthropic is also refunding users for any charges it identifies as unauthorized.BREAKING: Anthropic is signing Claude users out and deleting their saved card because infostealer malware on their machines handed a bad actor live Claude login sessions. Anthropic says its systems detected the activity, and the notification names six stealer families across… pic.twitter.com/0nX53PaeiH— International Cyber Digest (@IntCyberDigest) August 29, 2026“”Our systems detected this activity on your account, and we’ve therefore removed your card on file and signed out the sessions involved to help block further unauthorized access.” continues the report. “If your usage limits looked like they refilled and then drained while you weren’t using Claude, this was likely the cause.””Anthropic identified Vidar, LummaC2, StealC, RedLine and Acreed on Windows, plus Atomic Stealer on a small number of Macs. The company revoked affected Claude sessions, forcing users to log in again, and removed saved payment methods to prevent unauthorized charges. Existing plans will continue until the current billing period ends. After that, users will need to add their payment method again. Anthropic may also sign them out again if it detects suspicious activity.If you use Claude and haven’t checked your usage history recently, that’s worth doing today rather than next week. Anthropic’s advice is the standard but genuinely necessary response: run a full malware scan before logging back in, change your account password with two-factor authentication enabled, and treat any pirated download or unofficial app installer with the same suspicion you’d give a sketchy email attachment. An AI subscription being quietly drained isn’t the scariest thing an infostealer can do to you, but it’s a pretty reliable sign that something considerably worse, like your actual banking credentials, might already be sitting in the same haul.Follow me on Twitter: @securityaffairs and Facebook and MastodonPierluigi Paganini(SecurityAffairs – hacking, Anthropic)