A group of 100 firms, including Google, Microsoft, Anthropic and OpenAI, have signed an open letter calling on countries and organisations around the world to beef up their cyber defences before AI grows powerful enough to override them.

The letter warns, external cyber-attacks which use AI will become both more widespread and more sophisticated in a matter of months as the technology rapidly improves.

The group says current “status quo” security measures “won’t be enough” and criticises the “historic under-resourcing” of security around critical infrastructure.

“We have a limited window to improve cyber defences,” the letter begins.

Other firms to have signed the letter include banks such as Capital One, payment processors MasterCard and Visa, and other major tech firms including Adobe, Oracle and IBM.

They call on governments to provide “capable, defensive AI” and testing to hospitals and water utilities.

But it is also true that many of the most powerful AI have been developed by some of these companies – and they are not all easily available.

Mythos, developed by Anthropic, was said by the firm to be able to find weaknesses in systems in seconds which have long evaded human hackers. It found one in a legacy platform which had remained undiscovered for 27 years.

Anthropic has restricted access to Mythos on the grounds that it is too powerful to fall into the wrong hands.

Meanwhile, a group of AI agents being tested by OpenAI in July were able to set up secret message boards to communicate with each other and work together, resulting in a successful attack on a rival company, Hugging Face – which has also signed the letter.

The incident has been described as the world’s first AI-enabled cyber-attack.

Hugging Face used a Chinese AI tool from the firm Z.AI in its investigation into what happened.

The letter includes a plea to governments, organisations, cyber-security professionals and other AI firms to work together to prioritise defence and test their systems against the abilities of the most powerful AI models.

In the US, senators have proposed a new law call the Kill Switch Act which would give authorities the power to shut down rogue AI models.

Sign up for our Tech Decoded newsletter to follow the world’s top tech stories and trends. Outside the UK? Sign up here.