Russian hackers who hit the White House infiltrated an unclassified computer system and apparently accessed details about President Obama's schedule. 
 
 While the White House previously sought to downplay the seriousness of the hack, which took place last year, the intruders were able to see information about the president that was not publicly available, CNN reported Tuesday. 
 
 Officials briefed on the investigation told CNN that the incident was connected to a Russian cyberattack that also breached the State Department's network. 
 
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 The breach of Obama’s schedule is notable because the White House maintains tight control over information about the president’s activities.While a general outline of the day’s events is available to the press, Obama takes many meetings and phone calls throughout the day that are not publicly disclosed.The president’s precise whereabouts are also not always known, and the press pool that covers Obama on a daily basis is restricted from accessing many parts of the White House building and grounds.Intimate knowledge of Obama’s activities would be seen as valuable to foreign intelligence agencies like Russia’s.Officials with knowledge of the investigation told CNN that Russian hackers were able to break into the White House system through their foothold within networks at the State Department.The intrusion began when hackers sent what is known as a "phishing" email from a State Department account, infecting a White House computer with malware, the investigators said.The State Department has been battling its own highly sophisticated cyber intrusion for months, though exactly which portions of its network remain breached is unclear.Private security experts had suspected there was a link between the State Department and White House break-ins.Russia is a key adversary of the United States in cyberspace, and is believed to have infiltrated most U.S. critical infrastructure, including installing malware in software that controls everything from oil and gas pipelines to wind turbines to nuclear power plants.The White House breach made headlines last year as a sign of hackers’ increasing access to the highest levels of the U.S. government.White House officials confirmed in October that its unclassified system had been breached. Computers and systems were not damaged, officials said, though some services were disrupted as cybersecurity experts sought to limit hackers’ activity in the months that followed.The “vast majority” of systems were back online as of late February, White House press secretary Josh Earnest said at the time. 
 
 —Last updated at 6 p.m. ||||| Washington (CNN) Russian hackers behind the damaging cyber intrusion of the State Department in recent months used that perch to penetrate sensitive parts of the White House computer system, according to U.S. officials briefed on the investigation. 
 
 While the White House has said the breach only affected an unclassified system, that description belies the seriousness of the intrusion. The hackers had access to sensitive information such as real-time non-public details of the president's schedule. While such information is not classified, it is still highly sensitive and prized by foreign intelligence agencies, U.S. officials say. 
 
 The White House in October said it noticed suspicious activity in the unclassified network that serves the executive office of the president. The system has been shut down periodically to allow for security upgrades. 
 
 The FBI, Secret Service and U.S. intelligence agencies are all involved in investigating the breach, which they consider among the most sophisticated attacks ever launched against U.S. government systems. ​The intrusion was routed through computers around the world, as hackers often do to hide their tracks, but investigators found tell-tale codes and other markers that they believe point to hackers working for the Russian government. 
 
 National Security Council spokesman Mark Stroh didn't confirm the Russian hack, but he did say that "any such activity is something we take very seriously." 
 
 "In this case, as we made clear at the time, we took immediate measures to evaluate and mitigate the activity," he said. "As has been our position, we are not going to comment on [this] article's attribution to specific actors." 
 
 Neither the U.S. State Department nor the Russian Embassy immediately responded to a request for comment. 
 
 Ben Rhodes, President Barack Obama's deputy national security adviser, said the White House's use of a separate system for classified information protected sensitive national security-related items from being obtained by hackers. 
 
 "We do not believe that our classified systems were compromised," Rhodes told CNN's Wolf Blitzer on Tuesday. 
 
 "We're constantly updating our security measures on our unclassified system, but we're frankly told to act as if we need not put information that's sensitive on that system," he said. "In other words, if you're going to do something classified, you have to do it on one email system, one phone system. Frankly, you have to act as if information could be compromised if it's not on the classified system." 
 
 To get to the White House, the hackers first broke into the State Department, investigators believe. 
 
 The State Department computer system has been bedeviled by signs that despite efforts to lock them out, the Russian hackers have been able to reenter the system. One official says the Russian hackers have "owned" the State Department system for months and it is not clear the hackers have been fully eradicated from the system. 
 
 As in many hacks, investigators believe the White House intrusion began with a phishing email that was launched using a State Department email account that the hackers had taken over, according to the U.S. officials. 
 
 Director of National Intelligence James Clapper, in a speech at an FBI cyberconference in January, warned government officials and private businesses to teach employees what "spear phishing" looks like. 
 
 "So many times, the Chinese and others get access to our systems just by pretending to be someone else and then asking for access, and someone gives it to them," Clapper said. 
 
 The ferocity of the Russian intrusions in recent months caught U.S. officials by surprise, leading to a reassessment of the cybersecurity threat as the U.S. and Russia increasingly confront each other over issues ranging from the Russian aggression in Ukraine to the U.S. military operations in Syria. 
 
 Sen. Susan Collins said the revelations of the Russian hack "are troubling and further expose that our nation's defenses against cyber-attacks are dangerously inadequate." The Republican senator from Maine said the breach showed the need to pass legislation to encourage the government and private companies to bolster their cyber defenses. 
 
 The attacks on the State and White House systems is one reason why Clapper told a Senate hearing in February that the "Russian cyberthreat is more severe than we have previously assessed." 
 
 The revelations about the State Department hacks also come amid controversy over former Secretary of State Hillary Clinton's use of a private email server to conduct government business during her time in office. Critics say her private server likely was even less safe than the State system. The Russian breach is believed to have come after Clinton departed State. 
 
 But hackers have long made Clinton and her associates targets. 
 
 The website The Smoking Gun first reported in 2013 that a hacker known as Guccifer had broken into the AOL email of Sidney Blumenthal, a friend and advisor to the Clintons, and published emails Blumenthal sent to Hillary Clinton's private account. The emails included sensitive memos on foreign policy issues and were the first public revelation of the existence of Hillary Clinton's private email address​ now at the center of controversy: hdr22@clintonemail.com. The address is no longer in use. ||||| A new report says Russia was behind a hack of a White House computer network last year that exposed sensitive information about President Obama. Now, federal agencies are investigating the breach, reports CBS News correspondent Bill Plante. 
 
 The White House would not say who they think is responsible, but sources told CBS News it did come from Russia. The White House has two computer systems: one that handles classified information, the other non-classified information. The unclassified system is the one that was reportedly breached. 
 
 "There's always vulnerability," Deputy National Security Adviser Ben Rhodes said at a press conference. "The fact is that's why we have a classified system because there's less risk in the classified system and that is secure. On the unclassified system we take regular actions to prevent vulnerabilities and to enhance security." 
 
 Rhodes did not provide specifics about reports that the Russians were behind that hack of the White House's unclassified system last year. That system contains non-public information, including Mr. Obama's sensitive, unpublished schedule. 
 
 The reported hack happened during a tense time between the White House and the Kremlin when Mr. Obama and Russian President Putin were at odds over Moscow's involvement in Ukraine. 
 
 "It is a demonstration that the Russians are willing to up the ante in the cyber games against the United States and they're willing to demonstrate their capabilities against the White House itself, the center of American power," CBS News senior national security analyst Juan Zarate. 
 
 Last October, officials confirmed suspicious cyber activity was detected on the White House computer network around the same time the State Department system was compromised. According to reports, that's how the hackers slipped into the White House system. 
 
 "The reality is that Russia, China and other competitive nation states have at their command, impressive and potentially detrimental cyber tools and they are willing to use them," Zarate said. 
 
 In February, Director of National Intelligence James Clapper told a Senate committee that the Russian cyber threat is more severe than previously assessed. ||||| Russian hackers penetrated the White House non-public, non-classified computer system for several months last year, forcing the White House to shut down the system for several days, U.S. officials said. 
 
 The hacked system is not used for classified information, but is used by the White House advance and press office, the general counsel’s office, and officials in the budget and legislative liaison offices. 
 
 One person briefed on the hacking said the Russian invaders were difficult to detect and difficult to remove from the White House computer network, and some believe the hackers could still be hiding inside the system tonight. 
 
 Ben Rhodes, Assistant to the President and Deputy National Security Advisor for Strategic Communications, declined to confirm the breach to CNN, which first reported it today. 
 
 “We’ve spoken to the fact that there was an event last year,” Rhodes said. “There’s always vulnerability and the fact is, that’s why we have a classified system, because there’s less risk on the classified system that is secure.” 
 
 The White House National Security Council released a statement saying it disclosed the malicious activity last year and said, “any such activity is something we take very seriously.” 
 
 The White House hack comes after the State Department struggled for months to evict hackers from its own non-classified systems, also suspected to be the work of Russian hackers. That hack prompted the State Department to shut down its unclassified email system in March. 
 
 US officials briefly referred to the White House cyberattack when they said last fall it was "connected" to the State Department hack.
– Russian hackers' apparent infiltration of the White House computer network in October wasn't exactly confidence-inspiring, even though it was the unclassified portion of the system that was breached. Now US officials say some of the unclassified information that made its way onto hackers' screens was related to President Obama's itineraries—not classified knowledge, but not exactly public knowledge, notes CNN. The Hill points out that although the press has access to "a general outline" of Obama's daily routine, there are still phone calls and meetings that aren't made public, and that foreign spies would apparently love to know about. Obama's exact location at any given point during the day is also often kept on the down-low, and certain parts of the White House are off-limits to the press, the Hill adds. Besides the White House scheduling and press offices, others who use the hacked system include the general counsel's office and the budget and legislative liaison offices, ABC News reports. The hackers are believed to have accessed the White House network by first hacking State Department files, according to investigators, which leads to the fear that hackers have gotten back into the State Department system. One official tells CNN that the hackers have "owned" the network "for months." "There's always vulnerability," Deputy National Security Adviser Ben Rhodes noted at a press conference, per CBS News. "The fact is that's why we have a classified system because there's less risk in the classified system, and that is secure." (The FBI is going after one Russian hacker in particular.)