A cyber-attack on Germany's government IT network is "ongoing", officials say, a day after they said it had been "brought under control".
"It is a very serious cyber-attack," said Armin Schuster, who chairs the parliamentary committee that oversees the intelligence services.
The defence and interior ministries' private networks are being affected.
The officials did not confirm 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.
Russia has not commented on the issue.
"It is an ongoing affair, an ongoing attack," Mr Schuster said on Thursday.
"So a detailed public discussion would simply be a warning to the attacker which we do not want to make," he added.
Members of parliament have complained 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 allowed the hackers controlled access in order to track culprits and observe 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 thought to have targeted the Christian Democratic Union party of Chancellor Angela Merkel.
The group is also believed to be behind breaches in the US presidential elections in 2016.