Hackers targeted an unclassified White House network in recent weeks but did not damage any systems, according to news reports.
The intrusion, however, resulted in temporary disruptions in regular services while cybersecurity teams moved to contain it, according to The Washington Post, which quoted White House officials speaking on condition of anonymity.
The "activity of concern" was found in the unclassified Executive Office of the President (EOP) network. There is no evidence to date that the classified network was also breached, according to the report.
The hackers are thought to be working for the Russian government, the Post said, citing unnamed sources. The U.S. was alerted about the breach by an ally, the report said.
U.S. government officials could not be immediately reached for comment after business hours.
Security firm FireEye said in a report that Russia could be behind a computer spying campaign, directed at targets of interests to Russia such as European governments, militaries and security organizations. The attacks by the group FireEye dubbed as APT28 leave less clues than other state-backed attacks, it said.
Reuters also reported Tuesday that suspicious activity had been reported on the network used by EOP employees. It quoted an unnamed official as saying that measures to counter the activity had resulted in "temporary outages and loss of connectivity for some EOP users."