Wed Jun 10, 2015 2:59pm EDT Berlin

A cyber attack on the German Bundestag lower house of parliament reported last month is still stealing data and could force officials to spend millions of euros replacing the entire computer system, German media reported on Wednesday.

The online edition of news magazine Der Spiegel also quoted what it said were experts from an internal investigation saying there were indications that a Russian intelligence agency had staged the attack.

A spokesperson for the Bundestag could not be reached for comment and there was no immediate response from Moscow. Parliamentary and security sources in Berlin told Reuters that the reports were "plausible".

Replacing more than 20,000 new computers could cost several million euros and take months, the daily Sueddeutsche Zeitung and German television network ARD reported.

The media reports said that the hackers were still receiving data from the Bundestag computers.

"The trojans are still active," the Spiegel online edition quoted a parliamentary source as saying, referring to "trojan" attacks where users are tricked into installing software that can steal data from their computers.

A parliamentary spokeswoman announced in May that unknown hackers had tried to get into the data network.

In January, German government websites, including Chancellor Angela Merkel's page, were hacked in an attack claimed by a group demanding Berlin end support for the Ukrainian government, shortly before their leaders were to meet.