The company confirmed that the compromised data includes customers' names, addresses and phone numbers.
Details on several celebrities, politicians and business leaders are reportedly among the items. No customer credit card information or bank details are believed to have been compromised in the theft.
The breach occurred in 2006, but news of the data loss only came to light when Der Spiegel magazine found the details being offered by a third party.
Word of the breach is bad news for Deutsche Telekom. The company came under intense pressure from the German government earlier this year after Der Spiegel broke the news that the operator was using private investigators to spy on journalists and directors suspected of leaking information on the company's restructuring plans.
T-Mobile loses 17 million customer details
By Shaun Nichols on Oct 9, 2008 3:21PM