600,000 bank cards stolen: three AIs compromised hundreds of online stores

Cybercrime is changing scale. According to researchers at Gambit Security, an unprecedented hacking campaign, orchestrated almost entirely by artificial intelligence agents, targeted hundreds of online stores during the summer of 2026. The provisional toll: at least 119 merchant sites compromised and more than 600,000 bank cards stolen, numbers that were still valid.

One troubling detail: the attack was reportedly not carried out by a team of experienced hackers, but by a single individual, described as living in China. That person’s role would have been limited to a few brief instructions, before leaving three AI agents to work on their own for hours.

An almost fully autonomous cyberattack

Gambit Security’s investigation draws in particular on analysis of the command server used by the attacker. The researchers describe an operation that was almost entirely autonomous, without continuous human supervision.

In practice, the cybercriminal would have assigned objectives to the AI agents, then let them act. Those agents would have scanned, exploited and compromised merchant sites with unusual efficiency. For experts, the case marks a threshold: autonomous AI agents would now be capable of running an attack from end to end.

Strix, Cairn and Hermes: the AI trio behind the attack

Three AI agents, described as open source, would have coordinated the offensive.

• Strix scanned sites for security flaws.
• Cairn took over to exploit vulnerabilities automatically until it obtained administrator access.
• Hermes acted as conductor. It ran the campaign, made the strategic decisions and directed the other two agents.

Hermes relied on Anthropic’s Claude Opus 4.6 model. Between 10 and 15 September, the attacker reportedly launched 105 attacks using this procedure. In five days, at least 27 companies would have been hacked by the trio.

According to Gambit Security, once access was obtained it generally took less than a day to compromise the target. In many cases, a few hours would have been enough.

119 merchant sites compromised

The researchers counted 119 affected merchant sites. Presumed victims include:

• a major hotel chain listed in the Fortune 500;
• a large American airline;
• an industrial distributor;
• an online fashion retailer.

On these sites, the AIs would have injected skimming scripts. This malicious code, slipped directly into checkout pages, intercepts card data at the moment of purchase. The shopper enters card details without realizing they are captured in real time.

On one American merchant site, the attackers would even have set up an automated task able to reinject the malicious script every two minutes after it was removed.

Cleanup, erased backups and collateral damage

Another finding from the researchers: the agents were reportedly ordered to cover their tracks after the attack. Once the data had been stolen, they were to delete the card details directly from the databases of the compromised sites.

That instruction, found in Hermes’s configuration files, would have caused collateral damage. In some cases, internal backups were erased, creating the impression that ransomware had passed through.

A tiny cost for a highly profitable operation

Gambit Security estimates that the attacker spent between $12,000 and $18,000 over two months to orchestrate this cyberattack. The operation used pay-as-you-go AI models: the more the agents were asked to break into sites, the higher the bill.

Spread across the number of targets, the cost would come to about $25 per company attacked. The cheapest target would have cost only $3. Given the volume of bank cards siphoned off, the attack can be considered extremely lucrative.

Why this AI cyberattack changes the stakes

Until now, a large-scale hacking campaign required a team of seasoned cybercriminals, time and sharp technical skill. With tools such as Strix, Cairn and Hermes, a lone attacker, even one with limited skills, could now launch a complex operation and draw substantial profit from it.

For e-commerce sites, the case is a reminder to strengthen:

• monitoring of scripts present on payment pages;
• regular security audits;
• protection of customer databases;
• detection of abnormal behavior;
• isolated, immutable backups.

The researchers note, however, that the attack is still under way. In other words, the toll of 119 compromised sites and 600,000 stolen bank cards could still grow.

FAQ

How many bank cards were stolen?

More than 600,000 unexpired bank card numbers were reportedly stolen.

How many e-commerce sites were compromised?

Researchers identified at least 119 merchant sites.

Who is behind the attack?

The investigation points to a lone cybercriminal, described as living in China, who would have used three AI agents.

Which three AI agents were involved?

Strix, Cairn and Hermes. Hermes relied in particular on Anthropic’s Claude Opus 4.6.

Is the attack over?

No. According to Gambit Security, the attack is still ongoing.

What to remember

This AI-driven cyberattack shows that autonomous agents are no longer mere assistance tools. They can now scan, exploit, infect and clean up infrastructure at scale, with minimal human involvement. For online stores, the threat is no longer only technical: it is becoming industrial, automated and extremely profitable.