Last year, some of President Obama's emails were exposed to Russian hackers during a White House computer system breach. Although the hackers managed to delve deeply into the unclassified system, no classified networks were compromised, The New York Times reports. Servers that control the traffic to Obama's BlackBerry also remained secure.

According to officials familiar with the investigation, the hack largely affected people inside the White House with unclassified email archives and communications, the Times reports. Obama's personal email account was not affected, rather, much of his correspondence was culled from the accounts of people with whom he communicated frequently.

The White House is hit with cyberattacks daily

The White House is hit with cyberattacks every day, the Times reports, but this was an advanced, highly targeted attack. "This has been one of the most sophisticated actors we’ve seen," a senior official told the Times.

Earlier this week, the Pentagon disclosed that Russia had hacked its own unclassified networks this year, but the White House hasn't given details about any similarities between the two events.

Many top-level employees in the White House have two computers: one operating on a secure, classified network, and the other on an unclassified network, the Times reports. However, it's possible that sensitive information, including policy issues and scheduling, made their way onto the unclassified network.

Senior officials have known the severity of the breach for months, but just revealed it to the public this week, the Times reports. There are no details on how many emails the hackers obtained, or if they contained sensitive information.