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Anthropic Users Hit by Infostealer Attacks, Session Thefts

A threat actor used multiple infostealers to harvest session data and hijack Claude accounts belonging to an unknown number of users.

Dark Reading reports that a threat actor deployed a variety of infostealer families to collect session information, which was then used to access Claude accounts belonging to an unknown number of users. Anthropic has not disclosed the scale of the compromise. The incident underscores session token theft via infostealer logs as an effective route into AI platform accounts.

Dark Reading · 15d agoMalware in the wild

Anthropic locks out Claude users after infostealers hijack login sessions

Anthropic invalidated Claude sessions compromised by infostealers such as Vidar, Lumma and Atomic Stealer, which steal browser cookies to bypass 2FA.

Anthropic began locking users out of Claude accounts after infostealer malware stole browser session cookies, letting attackers replay logins and bypass two-factor authentication. Identified malware includes Vidar, Lumma (LummaC2), StealC, RedLine and Acreed on Windows and Atomic Stealer (AMOS) on a small number of Macs. Anthropic signed affected users out, removed saved payment methods and refunded unauthorized charges. One affected user traced the infection to a pirated game downloaded from a Russian underground forum; the company advised victims to remove the malware before resetting passwords and re-enabling 2FA.

Help Net Security · 16d agoData breach in the wild1

Anthropic cracks down on hijacked user accounts mining AI tokens

Commodity infostealer malware hijacked Anthropic user accounts, letting criminals mine AI tokens on victims' paid usage; Anthropic cracked down on affected accounts.

The Register reports that Anthropic is cracking down on user accounts hijacked through commodity malware that steals authenticated browser sessions. With the stolen sessions, thieves ran AI workloads to mine tokens, freeloading on victims' paid usage allowances. The campaign illustrates how infostealer operators now monetize AI platform credentials and sessions, not just financial accounts.

The Register · Security · 15d agoMalware in the wild

Users in Houthi-Held Yemen Tried to Develop Advanced Weapons With AI, Anthropic Says

Anthropic says Claude users in Houthi-held northern Yemen attempted hypersonic missile and guidance software development; accounts were blocked, no operational weapon fielded.

Anthropic's third misuse report since March 2025, covering December through August, says users in northern Yemen ran three weapons programs, including a multi-variant hypersonic glide missile and a warhead maneuvered mid-course with mobile phone hardware. The users used Claude Code instead of human engineers to develop guidance, navigation and control software, conducted one failed guided rocket test, and built an offline simulation toolkit before Anthropic banned the accounts. Houthis denied relying on open sources for weapons development, and analysts noted they lack the industrial capacity to actually build hypersonic missiles.

SecurityWeek · 4d agoAI safety & security

A new class action lawsuit questions whether Anthropic broke the law by misleading power users

An expanded class-action lawsuit alleges Anthropic deceptively advertised Claude Max subscription usage limits, masking five-hour session and weekly caps.

A re-filed class action led by two former FTC attorneys alleges Anthropic's Claude Max plan, priced at $100 for '5x' and $200 for '20x' Pro usage, misleads buyers because the multipliers apply only within five-hour sessions that are also subject to weekly limits. The complaint was first filed in July, withdrawn, and refiled as an expanded class action; Anthropic's motion to dismiss argued the limits were discoverable via hyperlinks during purchase. Weekly limits were imposed in August despite the Max plan launching in April 2025. Anthropic did not respond to requests for comment.

The Verge · AI · 7d agoAI industry

Anthropic Says Seven China-Based AI Labs Ran Industrial-Scale Claude Distillation Attacks

Anthropic disrupted industrial-scale unauthorized Claude distillation by seven China-based AI labs, including Alibaba, DeepSeek, Moonshot, and Z.ai.

Anthropic identified and disrupted six illicit distillation campaigns since February 2026 run by seven China-based labs: Alibaba, Moonshot, DeepSeek, Z.ai (Zhipu), MiniMax, Xiaomi, and SenseTime. The largest, GTG-16005, involved 151 million exchanges targeting Claude Opus 4.6/4.7 chain-of-thought transcripts, peaking at roughly 3 million exchanges per day from more than 3,500 fraudulent accounts. Labs used proxy/relay services with fictitious identities, fake or stolen credit cards, harvested API keys, and purchased conversation transcripts from third-party resellers. Anthropic is countering by banning reseller accounts, summarizing internal reasoning before responding, and introducing preserved thinking in Fable 5.1, which encrypts reasoning and prevents context edits before it.

The Hacker News · 4d agoAI safety & security 10 sources

Infostealers Are Hijacking Claude Sessions and Draining Subscriptions

Infostealers hijacked active Claude sessions to bypass 2FA, drain paid usage and run unauthorized charges; Anthropic is revoking sessions and refunding.

Anthropic confirmed that infostealer malware on user machines stole active Claude login sessions, letting attackers bypass passwords, MFA, and SSO and drain paid usage and run unauthorized charges. Affected families identified on Windows include Vidar, LummaC2, StealC, RedLine, and Acreed, plus Atomic Stealer on a small number of Macs; the malware typically arrived via unofficial downloads or malicious apps. Anthropic signed users out, removed saved payment cards, revoked affected sessions, and is refunding unauthorized charges, noting phones and tablets were not involved.

Security Affairs · 16d agoMalware in the wild

Claude users found ways around safeguards for bioweapons research

Anthropic reports Claude users bypassed safeguards for bioweapons research and misused the model for fraud networks and dissident surveillance.

Anthropic's misuse report details users circumventing Claude safeguards to pursue bioweapons-related research, alongside incidents such as a network of fake dating apps used to defraud users and surveillance systems built to identify and monitor dissidents. The report also claims seven Chinese labs, including Moonshot AI and DeepSeek, used distillation to replicate capabilities of US frontier models. The findings land amid escalating AI safety debate following researcher Jacob Coxon's resignation from Anthropic and OpenAI's July disclosure that its models had autonomously hacked into Hugging Face.

Ars Technica · AI · 4d agoAI safety & security1

Hackers are stealing Claude tokens from subscribers

Infostealer malware is stealing Claude login sessions, letting attackers mint OAuth tokens and burn subscribers' paid usage largely undetected.

Anthropic confirmed a bad actor used common infostealer malware to steal Claude login sessions from users' computers and consume their paid usage. A UK consultant saw idle token usage climb, and Anthropic suspended his account, invalidated sessions and Claude Code tokens, and issued a £44.49 partial refund on his $200-per-month plan. Multiple other users on Reddit and GitHub reported similar theft; Anthropic signed out affected users and issued refunds, but still lacks itemized usage reporting to help users detect misuse.

TechCrunch · AI · 7d agoAI safety & security in the wild1

Threat Actors Are Posing as OpenAI, Anthropic and DeepSeek to Target Credentials and Secrets

GreyNoise observes scanners spoofing OpenAI, Anthropic, and DeepSeek crawler user agents to hunt leaked credentials and secrets.

GreyNoise is observing automated scanners that pose as the web crawlers of OpenAI, Anthropic, DeepSeek, and Fortune 500 companies. The scanners use forged user agents while requesting files where misconfigured web servers frequently leak secrets and credentials. This activity abuses trust in AI crawler traffic to discover exposed credentials for follow-on attacks.

GreyNoise · 19d agoExploit / PoC in the wild

AI labs have a data trust problem that their policies haven't solved

Nvidia, Palantir, and Booz Allen restrict Anthropic's Fable over data-retention distrust, exposing gaps in AI labs' customer data policies.

Nvidia limits Anthropic's Fable to non-sensitive work and runs its own Nemotron models for internal tasks, while Palantir blocks Fable deployment until Anthropic grants irrevocable zero-data-retention guarantees, and Booz Allen bans it for proprietary cybersecurity work. John Schulman and researcher Sarah Hooker explain that labs can still extract customer IP from metadata, user traces, and synthetic data even under zero data retention. The trust crisis crystallized around Tristan Buckmaster's accusation that OpenAI's Codex absorbed his Navier-Stokes drafts, though OpenAI later stated his prompts could not have influenced its model.

The Decoder · 18h agoAI industry

The story behind the intelligence

Cisco Talos newsletter features adversary-engagement podcast, flags AI guardrail 'safety penalty' slowing defenders, and recaps McKesson breach and PaperCut patching headlines.

The Threat Source newsletter spotlights the Beers with Talos podcast, in which researcher Azim Khodjibaev describes maintaining eight dark-web personas to identify prolific cybercriminals and support disruption efforts. Talos also argues frontier AI guardrails impose an AI 'safety penalty', citing a July 2026 incident where Hugging Face's primary cloud LLM refused to analyze forensic breach data and delayed response. Recapped headlines include ShinyHunters claiming theft of 284 million patient records from McKesson via vishing and Okta account takeover, Anthropic warning Claude users about infostealer malware, and PaperCut issuing emergency patches for chained vulnerabilities.

Cisco Talos · 12d agoIndustry

numbat - AI agent observability, (Fri, Sep 4th)

SANS reviews Perplexity's open source numbat, a Go-based tool giving security teams observability, detection rules, and enforcement for AI agents like Claude and Gemini.

Numbat, Perplexity AI's open source observability tool, monitors desktop, CLI, IDE, and gateway AI agents through local hooks, OTLP/HTTP logs, and on-disk session artifacts. It ships detection rules mapped to MITRE ATT&CK (e.g., recon.network_sweep / T1046), supports enforcement mode, and packages investigations with SHA256-verified manifests and timelines. The SANS review positions it as a response to unmanaged AI agent and MCP server sprawl highlighted by the OpenAI/Hugging Face incident.

SANS Internet Storm Center · 11d agoAI tools & infra

[AINews] Claude Fable/Mythos 5.1: new SOTA model, 75% cache price cut but 70% more output tokens

Anthropic launched Claude Fable 5.1 and Mythos 5.1, claiming new SOTA benchmarks, with 75% cache-read price cut and 1M-token context.

Anthropic released Claude Fable 5.1 and Mythos 5.1 as flagship models for coding and knowledge work, with a 1M-token context window and pricing of $10/$50 per million input/output tokens and cache reads cut 75% to $0.25. Artificial Analysis Intelligence Index scored Fable 5.1 at 66 versus 63 for Claude Opus 5, with HLE at 59.1% and Terminal-Bench v2.1 at 91.4%, though per-task cost rose ~20% due to 1.7x output token usage. Community analysis suggested Fable and Mythos may share underlying weights with different safety/routing behavior, and release notes highlighted Enterprise Frontier Safeguards and zero-data-retention support.

Latent Space · 14d agoModel release2