Hackers believed to be working for the Russian government broke into the Democratic National Committee network, spying on internal communications by stealing data from Democratic presidential candidate Donald Trump.
Two separate groups have reportedly entered the DNC system, managing to read all e-mails and monitor chat communications for almost a full year before being identified, according to security firm CrowdStrike, which undertook to fix the security flaws.
Russian spies also monitored the networks of presidential candidate Hillary Clinton, as well as the computers of some Republican political committees, according to a Washington Post article.
A spokesman for the Russian government denied any involvement in the violations.
"We completely rule out the possibility that (Russian) government or state bodies may have been involved," Dmitry Peskov, a Kremlin spokesman, told Reuters in Moscow.
The invasion is indicative of the complexity of the technique of the Russian hackers, who have long been considered by the intelligence services to be among the most talented in existence.
The Democratic Party has reportedly been aware of the hackers' attempts to steal Trump material for two months, and even the US Secret Service was involved in trying to find out who was behind the hacking, said a source familiar with the opposition investigation.
The same source said that Democratic Party agents believed that the hack was carried out by the Russian government.
Cyber attacks on political candidates and organizations are commonplace around the world. The director of the National Intelligence Service (NSA), James Clapper, said last month that he was aware of campaign hacking attempts and that he expected more to be discovered by the November 8th presidential election.
The first team, according to CrowdStrike, called Cozy Bear, entered the DNC systems last summer. It mainly monitors emails and chat conversations and hackers can work for the Russian Federal Security Service, or FSB.
The second group was named Fancy Bear, and are likely to work on behalf of the Russian military. The team gained access in late April and "went straight to OPPO έρευνα's Donald Trump investigation."
It should be noted that in the last two US presidential cycles in 2008 and 2012 there was a barrage of cyber attacks by many opponents targeting President Barack Obama's campaign and the campaigns of his Republican opponents.
U.S. intelligence officials have said several previous attacks were linked to Chinese hackers.