Software created by Yandex permits developers to create apps for devices running Apple's iOS and Google's Android, systems that run the vast majority of the world's smartphones.

Insecurity experts say "metadata" may then be accessed by the Kremlin and used to track people through their mobiles.

Researcher Zach Edwards first made the discovery regarding Yandex's code as part of an app auditing campaign for Me2B Alliance, a non-profit. Four independent experts ran tests for the Financial Times to verify his work.

Yandex has acknowledged its software collects "device, network and IP address" information that is stored "both in Finland and in Russia," but it called this data "non-personalised and very limited."

It added: "Although theoretically possible, in practice it is extremely hard to identify users based solely on such information collected. Yandex definitely cannot do this."

You have to feel sorry for "Russia's Google" which has been playing a rather delicate game where it does not oppose Tsar Vladimir Putin's desire for greater control of the internet while at the same time not hackin off the rest of the world which is hammering it with sanctions.

The company said it followed "a very strict" internal process when dealing with governments: "Any requests that fail to comply with all relevant procedural and legal requirements are turned down."