The main data network is a system that was supposed to be particularly secure and is used by the chancellor's office, ministries and the Parliament.
The parliamentary committee, responsible for monitoring Germany's intelligence services, called a special session on Thursday, demanding information about the hacking, read a report in the New York Times.
He declined to give any further information and said, "A public discussion would serve as a warning to the attackers that we simply do not want to give them."
Germany's Interior Ministry confirmed the attack on Wednesday, describing it as "isolated" and having been "brought under control."
The security sources, as cited by some German news outlets, have widely blamed a Russian hacking group, backed by the Russian government.
Berlin, however, has not publicly said anything about it. (ANI)