Fake Claude Max giveaway harvests Google logins through a window it draws itself

Malwarebytes researchers found a fake Claude Max giveaway that uses a spoofed Google sign-in window to steal users' login credentials.

Stefan Dasic is the Malwarebytes researcher who analyzed the campaign.

The site says Anthropic has passed 100 million users and is thanking people by giving away 10,000 free one-month subscriptions to Claude Max, its highest-usage plan.

The fake window opens with a human verification step instead of a password field, which Dasic said may reassure visitors while helping to keep automated scanners away from the next stage.

The malicious functionality loads through a single line of code from an outside service that presents itself as a reusable sign-in widget and includes installation instructions.

Comments in the code are written in Russian and refer to the target as the victim.

One comment explains that dark-themed fake windows used to flash white while loading, so the widget fetches the correct color in advance to remove the flicker.

"The code appears to be a maintained, reusable product rather than something built for this one campaign," Dasic said.

Researchers have documented the browser-in-the-browser technique since 2022.

In June, Palo Alto Networks' Unit 42 reported a campaign that used draggable fake browser windows to target Microsoft 365 users.

Microsoft reported in June that it had seen phishing, malicious advertising and search-based campaigns impersonating ChatGPT, Claude, DeepSeek and Copilot; some claimed a payment had failed and sent victims to a fake checkout, while others offered app downloads that installed malware.

A compromised Google account gives attackers access to the victim's email and documents along with password reset messages for other services, and the same account can also be used to sign into Claude.

Claude's paid plans start at $20 a month and cost considerably more for higher usage limits, while free accounts have stricter limits.

Of the FAQ's statement that no payment details are needed, Dasic said: "That part is true, which helps make the offer persuasive. Many people associate scams with requests for card details, and this page never asks for them."

The page copies Claude's real logo and colors, displays invented five-star reviews, and has a long footer whose links lead almost entirely to genuine Anthropic pages; Malwarebytes says this is probably the most effective trust signal on the site and that it cost the operator nothing.

Malwarebytes reported a counter claiming fewer than 750 of the 10,000 slots remain, dropping by a few every several seconds, and said the number is generated inside the visitor's browser and resets when the page is reloaded.

Help Net Security's account of the same Malwarebytes research says the counter claims fewer than 760 of the 10,000 slots remain.

The address bar, padlock and everything inside the supposed window belong to the phishing page, not Google; Malwarebytes says the only address bar that matters is the one belonging to the actual browser at the top of the screen.

The Malwarebytes and Help Net Security reports do not state how visitors reach the page or how many people entered credentials.

Last month Malwarebytes research covered infostealers hijacking Claude accounts and using the victims' paid allowances.

The two published accounts of the same page give different remaining-slot figures, fewer than 750 and fewer than 760, which is consistent with the counter being generated per visitor in the browser.

At the $20 entry price for a paid Claude plan, 10,000 one-month subscriptions amounts to $200,000 of advertised giveaway.