Russian government hackers have breached the computer network of the U.S. Democratic National Committee and gained access to opposition research on Republican Donald Trump, the committee and security researchers say.
U.S. Representative Debbie Wasserman Schultz, chairwoman of the Democratic National Committee (DNC), confirmed the network breach, which was first reported by The Washington Post on June 14.
"When we discovered the intrusion, we treated this like the serious incident it is," Wasserman Schultz said in a statement. "Our team moved as quickly as possible to kick out the intruders and secure our network," she added.
The Virginia-based cybersecurity firm CrowdStrike Inc. said the DNC asked it to investigate a suspected penetration of its systems that began as early as the summer of last year. The firm said it quickly discovered evidence that two hacking groups tied to the Russian government were involved.
"Both adversaries engage in extensive political and economic espionage for the benefit of the government of the Russian Federation and are believed to be closely linked to the Russian government's powerful and highly capable intelligence services," CrowdStrike said.
The two groups were able to enter the DNC's system and read e-mail and chat communications, according to the committee and CrowdStrike.
The hackers were expelled over the past weekend in a major computer clean-up campaign, committee officials and experts said.
Kremlin spokesman Dmitry Peskov on June 14 denied the Russian government was involved.
"I completely exclude the possibility that [the Russian] government or government agencies are mixed up in this," Peskov was quoted by the state-run RIA Novosti news agency as saying.
U.S. officials were quoted as saying Russian spies also targeted the networks of Trump -- the presumptive Republican contender for the White House -- as well as Democratic presidential candidate Hillary Clinton and the computers of some Republican political action committees.
CrowdStrike said one of the hacking groups -- dubbed Cozy Bear -- that it identified in the attack on the DNC network had previously breached unclassified networks at the White House, the State Department, and the Joint Chiefs of Staff.
The other group -- called Fancy Bear -- has targeted public- and private-sector systems around the world over the past decade.
CrowdStrike added that the two groups breached the DNC network separately from one another.
U.S. National Intelligence Director James Clapper said last month that U.S. officials had reported indications that hackers from abroad were eavesdropping on U.S. presidential candidate and that more cyberthreats targeting the campaigns are expected.
In its worldwide threat assessment released earlier this year, Clapper's agency identified Russia as a top cyberthreat.
"Russia is assuming a more assertive cyberposture based on its willingness to target critical infrastructure systems and conduct espionage operations even when detected and under increased public scrutiny," the document states.
The previous two U.S. presidential campaigns -- in 2008 and 2012 -- featured a series of cyberattacks targeting President Barack Obama's campaign and those of his Republican opponents.
U.S. intelligence officials have previously said that many of those attacks were tied to Chinese hackers.
Trump has vowed to seek improved relations with Russia and China if he is elected to the White House, saying Washington and Moscow "should seek common ground based on shared interests."
Russian President Vladimir Putin has said the wealthy businessman and reality TV star "is a person who stands out -- talented, without any doubt."
Clinton has accused Trump of taking an insufficiently hard line on Russia, which has been hit with U.S. and EU sanctions for its military seizure and annexation of Ukraine's Crimean Peninsula in March 2014 and subsequent backing of separatists in eastern Ukraine.
"If Donald gets his way, they'll be celebrating in the Kremlin," Clinton said earlier this month.