The data was released on Friday and reveals sensitive personal data from private messages to Facebook login information, to the personal email address of German Chancellor Angela Merkel. The data was leaked in an "Advent-calendar style" which started as "doors" focused on TV personalities, followed by entertainers and lastly politicians.
Katarina Barley, the German justice minister, said: "Those responsible want to damage confidence in our democracy and their institutions".
The head of Germany's Federal Office for Information Security, Arne Schoenbohm, said the agency had been aware of individual cases of hacked data being posted online in December, but only appeared on a large scale Thursday evening.
It looks like the hackers got the passwords to Facebook accounts and Twitter profiles and worked their way up from there, said Simon Hegelich, a political scientist at Munich's Technical University who has studied the manipulation of social networks.
German media said a fax number and two email addresses used by Merkel had been published. She said those affected included deputies of all parties represented in the Bundestag Lower House of Parliament, leaders of the European Parliament as well as regional and local assemblies. Personal information from artists and journalists with leftist political leanings was also published.
The leak has affected also celebrities and journalists.
"Germany's government network is not affected but we are still investigating", he said.
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While some communications belonging to German President Angela Merkel were found among the documents, a government spokesperson told The Guardian that no sensitive information linked to Merkel had been leaked.
The data dates back to before October previous year, but there is so much, it's hard to tell at this stage how far back in goes. In an embarrassment to German security services, it emerged that the data had been released in a series of daily instalments since Dec 1 but went unnoticed by authorities until Friday.
Private chats, financial and contact details of Germany's Chancellor and her colleagues and opponents have been posted on Twitter.
Though the Twitter account was suspended, the hacker provided multiple back-up links for people to download the breached files.
UK-based expert Graham Cluley said the breadth of the latest hack suggested it was a co-ordinated effort involving a determined group over many months.
Also known as "Turla" or "Uruburos", the group, which targets state departments and embassies worldwide, is believed to have links to Russian intelligence.