(Bloomberg) — Criminal hackers doing the bidding of the Russiangovernment are believed to have hacked into a non- classified WhiteHouse computer network last year, according to a person withknowledge of the investigation.

An analysis of the malicious code and other evidence gatheredshow certain characteristics known to be used by criminal hackersworking under the sponsorship of the Russian government, said theperson who wasn't authorized to speak publicly about theinvestigation.

The White House intrusion, which some U.S. officials believe wascarried out by hackers who had earlier gained entry into StateDepartment computers, was likely a signal from the government inMoscow in retaliation for sanctions the U.S. has imposed on Russia,the person said.

The White House said in October that it had identifiedpotentially threatening activity on its computer network and triedto close off access. At the time, two U.S. officials who soughtanonymity said cybersecurity specialists suspected that theintrusion was carried out by either the Russian government orcriminal hackers.

The hackers may have gained access to White House data throughan earlier intrusion at the State Department, where officialsregularly use e-mail to communicate with colleagues, according toU.S. officials who spoke on condition of anonymity.

"As we made clear at the time, we took immediate measures toevaluate and mitigate the activity," Mark Stroh, a NationalSecurity Council spokesman, said in an e-mail.

Russian Response

The Russian embassy in Washington didn't immediately respond toa phone call seeking comment. Earlier, Russia rejected a report byCNN Tuesday that its government was involved in hacking anon-classified White House computer network that exposed sensitiveparts of the e-mail system.

"It has become a kind of sport to blame everything on Russia,"Kremlin spokesman Dmitry Peskov told reporters on a conference callon Wednesday. "But the key thing is that they wouldn't go searchingfor Russian submarines in the Potomac River, like it was the casein some other countries."

Deputy White House National Security Adviser Ben Rhodes saidTuesday on CNN that no classified information had been compromised,while declining to link any attacks to Russia.

U.S. intelligence officials say the pace and sophistication ofRussian-sponsored attacks have increased as tension over Ukrainehas grown and the U.S. has imposed economic sanctions onRussia.

–With assistance from Angela Greiling Keane inWashington.