Mobile phone and broadband provider Vodafone Deutschland has been the target of a large-scale data theft affecting the personal details of two million German customers.
Spokesman Alexander Leinhos said the attack was conducted by an unidentified IT systems administrator who worked for a company contracted by Vodafone.
Vodafone said that the stolen data included customers' names, addresses, date of birth and bank details. Credit card information and passwords were not stolen.
Vodafone said it regretted the incident and warned its customers to be on guard against unsolicited phone calls or emails from people seeking to exploit the stolen data.
The company has more than 32 million mobile phone customers and more than three million broadband subscribers in Germany.
It is a wholly owned subsidiary of Vodafone Group.