The New York Stock Exchange resumed floor trading Wednesday afternoon after an apparent technical issue halted trading in all symbols for nearly four hours.
Two U.S. officials said there was no indication of a cyber attack nor a connection between the stock exchange outage and a computer glitch that grounded thousands of United Airlines flights around the world earlier Wednesday. Two major cybersecurity firms, FireEye and Mandiant, also said the issue appeared to be the result of a technical glitch rather than hacking.
"It appears that today we had system malfunctions at United, at the New York Stock Exchange and at The Wall Street Journal," Homeland Security Secretary Jeh Johnson said Wednesday afternoon at a previously scheduled speech on cybersecurity. "I've spoken to the CEO of United, Jeff Smisek, myself. It appears, from what we know at this stage, that the malfunctions at Untied and the stock exchange were not the result of any nefarious actor."
"The issue we are experiencing is an internal technical issue and is not the result of a cyber breach," the NYSE said in a statement. "We chose to suspend trading on NYSE to avoid problems arising from our technical issue. NYSE-listed securities continue to trade unaffected on other market centers."
President Obama has been briefed on the outage, according to a senior administration official, and White House and Treasury Department officials are monitoring the situation. The FBI has offered assistance to the NYSE. "No further law enforcement action is needed at this time. The FBI will continue to monitor the situation," FBI New York spokesperson Kelly Langmesser said in a statement.
White House press secretary Josh Earnest said it was too early to assess the economic impact of the NYSE outage.
The exchange was investigating the issue that caused the halt, Reuters reported, citing a source. Trading stopped around 11:30 a.m. ET.
"It's not a good day. I don't feel good for our customers who are having to deal with the fallout," NYSE President Thomas Farley told CNBC.
The Senate Judiciary Committee held a hearing Wednesday on cybersecurity, with FBI Director James Comey and other officials testifying. In a joint statement to the committee, Comey and the officials called for increased encryption technology.
"The development and robust adoption of strong encryption is a key tool to secure commerce and trade, safeguard private information, promote free expression and association, and strengthen cybersecurity," the statement said. "The [Department of Justice] is on the frontlines of the fight against cyber crime, and we know first-hand the damage that can be caused by those who exploit vulnerable and insecure systems."
Comey's statement expressed concern that terror groups like the Islamic State of Iraq and Syria -- which uses social media to spread propaganda and recruit followers -- are increasingly turning to "private messaging platforms" to communicate. "These encrypted direct messaging platforms are tremendously problematic when used by terrorist plotters."
President Obama has also highlighted the need for more advanced cybersecurity for government computer systems, which have been targeted by hackers in recent weeks. “State and non-state actors are throwing everything they’ve got to try to breach these systems,” Obama said last month at a G7 summit in Germany, adding that hackers are looking to obtain intelligence, sabotage and steal information from government systems.
The NYSE said all open orders would be canceled, according to Reuters. The issues seemed to be limited to the NYSE floor, and the exchange said it did not affect the NYSE Arca and NYSE Amex/Arca Options.
The New York Stock Exchange issues follow tumult in the Chinese markets, where stocks have plunged in recent weeks. More than $3 trillion has been wiped from Chinese markets, sending waves of panic throughout the country.
The Nasdaq reported no technical issues and said it continues to trade NYSE-listed stocks.
Just after 8 a.m. ET on Wednesday morning, the NYSE put out an alert about "a reported issue with a gateway connection" affecting certain symbols. It put out a notice at 10:37 a.m. ET that the problem was resolved.
"It's been a little bit of a bumpy day. We had some technical problems even before the opening," said Art Cashin, director of floor operations at the NYSE, in a CNBC interview.
"This will not cause a move in any particular direction, so I would kind of wait it out and see what happens," he added.
A complete interruption of trading on the exchange due to a technical issue "has little precedent," the New York Times reported. The NYSE website lists seven closures since the founding of its predecessor exchange in 1817 related to world-changing events, including the assassination of President Abraham Lincoln and the terrorist attacks on Sept. 11, 2001.
Separately on Wednesday, The Wall Street Journal website experienced an apparent outage that was resolved by roughly 1 p.m.
NBC News' Kristen Welker, Pete Williams and Jonathan Dienst contributed. This story is developing. Please check back for further updates.