Three months after detecting some unauthorized activity within the U.S. State Department's email systems, government officials are still unable to clear the network.

The computer network was shut down in late October to ensure security. Prior to the State Department attack, the hackers initially targeted the White House computer network. Since then, other agencies fell victim, including the U.S. Postal Service and the National Weather Service. The U.S. Military confirmed that its systems were secured.

Temporarily, some U.S. officials were asked to stop using their official emails and use Gmail instead. There are assumptions that it could either be Russia or China that are initiating the privacy breaches, so the FBI started the investigation.

But three months later, three people familiar with the investigation told the Wall Street Journal that the government hasn't cleared the email systems of the State Department and that the hackers still have access to the network. The National Security Agency (NSA) is scanning the systems and blocking the hackers, but those steps are not enough because the hackers are still able to find a new entrance by altering the codes.

The sources added that the investigators are still unsure of the data taken.

"We deal successfully with thousands of attacks every day," State Department spokeswoman Marie Harf said in a written statement. "We take any possible cyber intrusion very serious as we did with the one we discussed several months ago and we deal with them in conjunction with other relevant government agencies."

Russia remains suspect because of the similarity of the malware to other tools linked to Moscow and that it might be related to the Ukraine crisis. The NSA is still tracing the origin of the attack, according to two sources of Bloomberg.

The Russian embassy and the FBI refused to comment on the investigation.