An Israeli tech firm has promoted its ability to access a vast trove personal data on servers belonging to companies such as Google, Facebook and Apple.

NSO Group, which made headlines earlier this year over reports its software could hack WhatsApp, has been telling potential clients it can access the data surreptitiously, without the knowledge of individual users or the tech giants themselves.

The Israeli company said it could also access Apple and Microsoft’s servers using the same method, the Financial Times reported.

The technique allegedly works by duplicating authentication keys from services such as Facebook Messenger and iCloud from an infected phone and then creating a virtual clone copy that can impersonate it.

The newspaper based its report on people who had attended a recent product demonstration by the Israeli company.

It is not known how many individual cloud accounts may have been targeted by the technique.

An NSO spokesperson said: “We do not provide or market any type of hacking or mass-collection capabilities to any cloud applications, services or infrastructure.”

But the FT noted that NSO did not specifically deny its technology allowed it to deploy the capability described in its product demonstrations.

Google did not comment on the report, while Facebook said it was reviewing the claims.

In separate statements, Amazon, Apple and Microsoft said their security systems were robust.