A cyber-attack on Germany's government IT network is "ongoing", officials say, a day after they revealed it had been taken care of.
Armin Schuster, who chairs the parliamentary committee that oversees the intelligence services said "It is a very serious cyber-attack."
The defence and interior ministries' private networks are being affected.
The officials did not validate media reports that a Russian hacking group known as "Fancy Bear" was responsible.
The group, which is also known as APT28 and is believed to be linked to Russia's GRU military intelligence agency, is reported to have targeted the federal government's internal communications network with malware.
"It is an ongoing affair, an ongoing attack," "So a detailed public discussion would simply be a warning to the attacker which we do not want to make," Mr Schuster said on Thursday.
Members of parliament have protested that they have been kept in the dark about the attack that according to German media was detected in December.
German security officials say they have permitted the hackers controlled access in order to track culprits and study their methods.
On Wednesday, a German interior ministry spokesman said the attack was "isolated" and had been "brought under control".
Fancy Bear was blamed for a similar attack on the lower house of the German parliament in 2015 and is believed to have targeted the Christian Democratic Union party of Chancellor Angela Merkel.
The group is also thought to be behind breaches in the US presidential elections in 2016.
