Hacking isn't the only cyberthreat facing the US.
Russian interference in US politics also includes espionage and the spread of fake news, America's top intelligence official told the Senate on Thursday. He was speaking at a hearing on Capitol Hill that came after politicians called for details about Russian cyberattacks targeting the presidential election, and as social media sites like Facebook grapple with their role as an outlet for fake news.
Russia hacked into the email accounts of Democratic Party officials using a sophisticated spear-phishing tactic known as Grizzly Steppe, Director of National Intelligence James Clapper said. Emails, including some reportedly stolen from John Podesta, an adviser to presidential candidate Hillary Clinton, were later distributed through WikiLeaks and became fodder for attacks against Democrats during the campaign.
Russia's growing use of fake news, part of an effort to disrupt the election, was even more disturbing, Clapper said. The spread of Russian propaganda was the most aggressive and direct attempt to interfere in a US election that Clapper said he's ever seen.
"It's a grave concern," Clapper said. Fake news "has been part of a multifaceted campaign that the Russians mounted" to affect the election's outcome.
The hearing comes as the US wrestles with how to deal with a growing number of countries building out their hacking capabilities. More than 30 countries, including China, Iran and North Korea, are developing cyberattack capabilities, such as spear-phishing and data deletion attacks.
Senators expressed their support for the intelligence community, which has been challenged by key Republican lawmakers and Donald Trump. The president-elect has tweeted that reports that Russia tried to hack the election are an effort to challenge his victory. During one of the debates before the election, Trump argued it could have been Russia, China or "somebody that sits on their bed that weighs 400 pounds." He maintains that there's no proof Russia was involved in the hacks of Democratic Party officials or the email leaks, an idea WikiLeaks founder Julian Assange repeated on Tuesday.
Assange also said Russia wasn't the source of the emails, a comment that Trump tweeted.
Republican House Speaker Paul Ryan and Republican Sen. Tom Cotton on Wednesday criticized Assange and voiced support for the US intelligence community.
Clapper also criticized Assange, saying earlier leaks by Wikileaks had put people in jeopardy. He voiced his support for the intelligence community and said he had confidence in their assessment that Russia was behind the political hacks.
A report on Russian interference is supposed to be made public next week.
Intelligence officials warned senators there's no way to make the US completely safe from cyberattacks. Nearly all networks and systems are inherently at risk to hacking, NSA Director Mike Rogers said. Threats could come from newly developed exploits or careless mistakes, but they can't be eliminated, he said.
Clapper went further. "If there is an internet connection, there is always going to be a vulnerability."
The best security officials can do is manage risk. Spreading awareness, so Americans don't get caught in the same phishing scam that reportedly ensnared Podesta, is one of the many things people can do to protect themselves, Clapper told the senators.
John McCain, a Republican senator from Arizona, said it was important to establish a policy on how to respond to cyberattacks. "Unless we demonstrate that the cost of attacking the US outweighs the perceived benefits, these attacks will only grow," McCain said.
On Dec. 29, President Barack Obama announced a series of sanctions against Russia for the political hacks, booting 35 Russian intelligence officers from the US. While Sen. Lindsey Graham, a Republican from South Carolina, suggested that Obama should have done more, Clapper said the sanctions sent a strong message to Russia.
Meanwhile, social media companies continue to struggle with their role in spreading fake news. Facebook, which been widely used to spread false stories, last month added fact-checking features and tools that let its nearly 2 billion users report hoaxes.
CNET's Laura Hautala contributed to this report.