More than one million customers of the French telecoms group Orange have had their personal data stolen.
Users of its online portal fell victim to the theft last month, with information such as telephone numbers and email addresses taken.
It is the second breach in three months for Orange.
The revelation comes at a time of intense scrutiny of companies’ cyber-defences, in the wake of a massive hack at US retailer Target.
The ‘Heartbleed’ bug has also been discovered, exposing weaknesses in a commonly used web encryption programme.