The Russian firm Kaspersky Lab said the hacking at three European hotels was so sophisticated, it must have been created by a government.

World powers and Iran have been holding talks on the fate of Iran's nuclear programme ahead of a 30 June deadline.

Switzerland and Austria have both opened investigations into the hacks.

The US, UK, France, Germany, Russia and China are seeking a final agreement to curtail Iran's nuclear programme in exchange for sanctions relief.

They fear Iran wants to build a nuclear bomb - something Iran strongly denies.

Israel is not a party to the negotiations although it feels particularly threatened by the possibility of a nuclear-armed Iran.

In March, the Wall Street Journal reported concerns by US officials that Israel had been spying on the behind-closed-doors talks.

At the time, Israel denied the claims it had been spying.

Kaspersky, and an American security firm, Symantec, believe the so-called Duqu 2.0 software was employed to gather information.