In a statement to the South China Morning Post, a spokesman said the agency's digital forensics team provided technical assistance to targeted departments. However, the agency declined to say which departments had been targeted and how. 

The Star report said affected agencies included Malaysia’s Civil Aviation Department, the National Security Council and Malaysia Airlines, which is majority owned by the Malaysian government.

Malaysian police were investigating the attack, the newspaper said. The information office of Malaysia's Ministry of Home Affairs, which overseas the Royal Malaysia Police could not be reached for comment on Wednesday.

Once the hackers gained access to the networks, the government departments registered a flood of outgoing e-mails, the report said. The outgoing e-mails included classified documents, the report said.

By the time the transmissions were blocked and the affected computers shut down, an unspecified amount of information had already been sent from Malaysian government computers to China, it said. 

Such a hacking attack is not technically difficult, but requires preparation, said Dhillon Andrew Kannabhiran, founder and CEO of Kuala Lumpur-based Hack In The Box, which organises IT security conferences.

The timing of the attack, one day after the plane went missing, meant that the attackers had the PDF malware ready to use to infect the Malaysian government computers, he said.

Kannabhiran said investigators could only trace the stolen documents to where they had been sent to, but that might not provide definitive clues to who hacked into the computers.

Stolen documents are often sent to "some other compromised machine belonging to an innocent victim not connected with the attacker”, he said.

Tim Ryan, managing director for cyber security at Kroll, said the hackers could have sent the data to China "shouldn’t assume that because the data was sent to a Chinese address that the Chinese were actually behind the attack". 

Flight MH370 went missing more than an hour after it took off from the Malaysian capital Kuala Lumpur in the early hours of March 8 bound for Beijing, sparking an international search for the plane.

China participated in the multinational search effort in the Indian Ocean, which has so far been futile. Acoustic signals suspected to have come from the missing plane’s black boxes indicated that the airliner left its route to China, turned southwest and crashed in the southern Indian Ocean.

Australia is leading the search effort assisted by the PLA navy ship Zhu Kezhen and private contractors, scouring the vast ocean floor off Australia’s western shore with sonar equipment.

Australian Prime Minister Tony Abbott said on Wednesday that a new underwater hunt for the missing Boeing 777 had a “reasonable chance” of finding the plane, adding that searchers would not give up easily.

Experts have used technical data to finalise the most likely resting place of the plane deep on the ocean seabed and are preparing for a more intense underwater search to find it.

“They are now going to search the entire probable impact zone which is, from memory, something like 60,000 sq km of the ocean floor, off the coast of Western Australia,” Abbott told the Australian Broadcasting Corporation.

Abbott has repeatedly said Australia will do its utmost to find the plane and help determine what went wrong with the Boeing 777 to provide closure to the families of those onboard and the flying public generally.

“We’re determined to do the right thing by the Australian families who lost their loved ones in this plane, we’re determined to do the right thing by all of the bereaved families,” he said.

“And we’ve got a long way to go before we’re going to give this one up.”

Among the 227 passengers on board, 152 were Chinese and six were Australians.

India in March rejected a Chinese request to enter territorial waters in the Andaman Sea in an effort to search for the missing jet, before search efforts switched to the area off the coast of Western Australia, over concerns that the request might be an excuse for military snooping.

Additional reporting by Agence France-Presse