"I can assure our clients: their data is safe with Deutsche Telekom. The misbehaviour of a few bad apples in the past does not change this fact," chief executive Rene Obermann told Bild am Sonntag newspaper.
"Our staff do good and proper work."
Obermann denied any personal involvement in the affair which has seen Deutsche Telekom admit to spying on its staff and journalists in 2005 and perhaps also 2006 in a bid to identify the sources of press leaks.
"I learnt of a first case of data abuse at Deutsche Telekom last summer and did not hide anything, but drew the necessary personal and organisational consequences.
"Everything else was put in the hands of the prosecutors investigating the matter," said Obermann, who took up his post in November 2006.
Der Spiegel news magazine reports in its edition to be published Monday that one payment to private detectives hired to track calls by executives to journalists was authorised by an office manager who worked for both Obermann and Klaus Zumwinkel, the former head of the company's supervisory board.
Responding to the report, Obermann said: "If this is the case, it happened without my knowledge.
"I neither saw such an account nor signed off on it. At the time I had only been in my post for a few days."
Prosecutors probing the latest damaging privacy invasion scandal to hit a big German company raided Deutsche Telekom's Bonn headquarters on Thursday.
Der Spiegel alleged that former Deutsche Telekom boss Kai-Uwe Ricke, who stepped down in 2006, and Zumwinkel were in the spotlight of prosecutors.
Quoting prosecution documents, Der Spiegel said a former Telekom security chief, Klaus Trzeschan, had alleged he had been ordered to spy by Ricke and Zumwinkel.
Another former Telekom security chief Hans-Juergen Knoke, who held the post from 1998 to 2004, alleged the company was already engaged in the practice under former boss Ron Sommer, who left the group in 2002.
Ricke, Zumwinkel and Sommer have denied knowledge of the spying.