Deutsche Telekom (NYSE: DT - News) was on Sunday hit by a fresh scandal over the way it handles confidential information after it admitted losing the personal details of 17m customers, the largest data theft to date in Germany.

The theft at the company's mobile operation T-Mobile included the names, addresses and mobile phone numbers of high-profile politicians, celebrities and business leaders, although no bank details or credit card numbers were disclosed.

The news dealt a blow to efforts to restore Deutsche Telekom's reputation following allegations that former management hired private detectives to spy on directors and journalists. It also handed fresh ammunition to the growing ranks of politicians in Berlin calling for tougher data protection laws.

The data breach was uncovered after Der Spiegel magazine said it managed to access customer information via a third party. Deutsche Telekom reported the theft to state prosecutors in 2006 but assumed there had been no dissemination of the data.

The company said it had conducted "extensive research" after the loss occurred but had found no indication that the data was available for sale on the black market.

However, it only brought the incident to the attention of the German interior ministry last week.

"We can only apologise to our customers," chief executive René Obermann told the Bild am Sonntag newspaper. "The whole thing is a very exasperating incident."

The company has set up a hotline to field any customer concerns but it said there was no evidence the data had been misused.

The Der Spiegel report revealed that among those people affected by the data breach were members of parliament, ministers, former federal presidents and business leaders. The German interior ministry said it was conducting a risk assessment to examine the implications of the breach.

T-Mobile said it has since improved data security measures, including much greater restriction of access rights to customer data.

For Mr Obermann, the admission that Deutsche Telekom had lost such critical information marked a new low for the former state telecommunications group's battered corporate image.

Prosecutors raided the company's Bonn headquarters in May as part of a probe into allegations that Klaus Zumwinkel, former chairman, Kai-Uwe Ricke, ex-chief executive, and six other employees had commissioned a spying campaign. The executives have denied any wrongdoing.

Deutsche Telekom admitted passing information to authorities that staff had in 2005 and 2006 ordered the monitoring of phone bills to find out who was leaking sensitive corporate information. Mr Zumwinkel had quit the company three months prior to the raid after he was named a suspect in a tax-evasion case.