Unknown hackers have attacked the French website of mobile operator Orange, stealing account details of more than 800,000 customers.
Customer records including email and postal addresses, names and phone numbers were accessed by the data thieves from the 'My Account' page of Orange.fr on 16 January, 2014.
Orange confirmed the attack but claimed that no passwords were taken and that the affected page was quickly taken down.
The data from around 3 per cent of customers in France was compromised. In a letter to its customers, Orange said that the security breach came as a result of a phishing scam.
"We would like to warn you to be prudent when dealing with suspicious solicitations by email, sms or telephone," Laurence Thouveny, director of customer relations at Orange, said in the letter.
Thouveny said that no further action is required by customers, and that the firm were only informing of the attack in the interests of transparency.
There is a concern that the data stolen could be used to commit further phishing attacks and Orange has urged customers to change their passwords to help protect against this.
"We sincerely regret this incident," Orange said in a statement. "More than ever, the security of our customers' data is a priority, and Orange is committed to protecting the data and privacy of our customers."