The leak targeted cross-party politicians, including those from the CDU, CSU, SPD, Green, FDP and Linke parties, as well as celebrities, such as rapper Sido and actor Til Schweiger.
The Federal Office for Information Security said that there were no indications that government communication networks had been hacked.
ARD said that, after a first review of the data, journalists had not detected any incriminating content.
A defence ministry spokesman said the armed forces were not affected either.
The true extent of damage caused by the leak is not yet known although Justice Minister Katarina Barley said it was a "serious attack".
Germany's Bild newspaper, in turn, cited sources in the BSI, the country's state security agency, as saying that the German government's secure internal network was not compromised in the hacking incident.
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Some of the data goes as far back as 2012, according to an expert on German politics who analyzed it today, and the newest dates back to October 2018.
The leak has been now branded as an act of "hacktivism", but foreign nation-state cyber intelligence groups have been known to mask influence operations as hacktivisim in the past. No one has claimed responsibility for the attack.
The Kremlin, responding to previous allegations of cyberattacks on foreign computer infrastructure, has denied any involvement and said the accusations are part of a Russophobic witch-hunt.
The German Chancellor is the most prominent politician to have fallen victim of the cyber attack. MPs and government officials had their contacts, home addresses, chat entries and personal messages hijacked and uploaded to a Twitter account in several packages.
The leaked data was released through links published on Twitter in the form of an advent calendar, beginning with information about German television comedian Jan Böhmermann on December 1 and ending with members of Chancellor Angela Merkel's center-right party and its Bavarian counterpart.
"Hacking attack against politicians: The BSI is now intensively probing the issue in close cooperation with other federal institutions", the BSI said on Twitter, adding that "according to what we know so far" the government's confidential networks were unaffected. "That will not succeed", said Lars Klingbeil, secretary general of the centre-left Social Democrats, Merkel's coalition partner.