The latest on halted trading at the New York Stock Exchange (all times Eastern):
Top U.S. law enforcement and security officials said they didn't see a link between the outages at the New York Stock Exchange Wednesday and the temporary grounding of United Continental flights and the temporary malfunction of the Wall Street Journal's website.
"We do not see any indication of a cyber breach or a cyber attack," FBI Director James Comey told the Senate Intelligence committee.
"I think the Wall Street Journal piece is connected to people flooding their web site in response to the New York Stock Exchange to find out what's going on. In my business, you don't love coincidences, but it does appear that there is NOT a cyber intrusion involved."
Homeland Secretary Jeh Johnson, speaking at the Center for Strategic and International Studies, said he had spoken to the CEO of United, Jeff Smisek.
"It appears, from what we know at this stage, that the malfunctions at United and the stock exchange were not the result of any nefarious actor. We know less about The Wall Street Journal at this point, except that their system is back up again, as is the United Airline system."
Trading has resumed on the New York Stock Exchange after an outage of more than three hours caused by technical problems.
There was no interruption at the dozens of other U.S. stock exchanges Wednesday, including the Nasdaq, so investors were still able to buy and sell stocks easily.
The NYSE didn't say what the problem was but described it as internal issue and not the result of a breach of its systems.
The market was already lower as traders worried about China's failure to halt a plunge in its shares and talks remained stuck between Greece and its lenders.
In the last hour of trading the Dow Jones industrial average was down 210 points, or 1.2 percent, at 17,569. The Standard & Poor's 500 index was off 25 points, or 1.2 percent, to 2,056.
Thomas Farley, president of the NSYE Group, which includes the New York Stock Exchange, told CNBC in an interview that the exchange was aiming to reopen before the usual market closing, which happens at 4 p.m. Eastern time.
Trading has been halted since 11:32 a.m. on the exchange because of a technical problem, the NYSE has said.
Officials and the exchange have said that there is no indication that the problem is the result of a cyber-attack. Officials have also said there is no sign that it is related to a computer outage that grounded United Airlines flights Wednesday morning.
White House spokesman Josh Earnest says President Obama was briefed on the technical problem that has halted trading on the New York Stock exchange by White House counterterrorism and homeland security adviser Lisa Monaco and chief of staff Denis McDonough.
He says Monaco told the president there is no indication that malicious actors are involved.
Earnest said the NYSE has been in close contact with the Department of Homeland Security, the Securities and Exchange Commission and the Treasury Department.
He says that despite indications that this was not a cyber-breach, "The administration is keenly aware of the risk that exists in cyber space right now."
The halt in trading on the New York Stock Exchange hasn't stopped trading of NYSE-listed shares, which continue to change hands on other exchanges.
Other exchanges compete for the orders made to buy and sell stocks.
Tom Caldwell, who runs an investment firm with stakes in several exchanges, says there are some 60 exchanges and trading venues that can take orders when one goes down, and so he isn't worried.
"It's disruptive, but not wildly disruptive," said Caldwell, chairman of Caldwell Securities. "You have so many competing exchanges."
The technical problem that has halted trading on the New York Stock Exchange hasn't changed the Dow or other market indexes much.
Stocks were already down when the trading halt occurred. Traders worried about China's failure to stop a steep drop in its own market, and they were also monitoring a logjam in talks between Greece and its creditors.
Major indexes continued to move as stocks were traded on other platforms such as the Nasdaq.
The S&P 500 was down 23 points, or 1.1 percent, to 2,057. The Dow Jones industrial average sank 184 points, or 1.1 percent, to 17,593, while the Nasdaq fell 66 points, or 1.3 percent, to 4,931.
It's not clear how long the trading halt, now two hours old, will continue.
Stock in the company that owns the New York Stock Exchange Is trading despite the halt on the floor, and it is falling.
The IntercontinentalExchange Group, which bought NYSE Euronext in late 2012, is down 1.7 percent. That compares with a drop of 1.1 percent for Standard and Poor's 500 index.
Stock of Nasdaq OMX Group, the company that owns the rival Nasdaq market, is down 1.8 percent.
Trading exchanges have been struggled with technical trouble in recent years like that which halted trading on the New York Stock Exchange on Wednesday.
In May 2010, the Dow Jones industrial average plunged hundreds of points in minutes due to mass selling triggered by computerized trading programs. In March 2012, BATS Global Markets, a Kansas company that offers stock trading services, canceled its own IPO after several technical snafus.
Two months later, a highly anticipated IPO of Facebook on the Nasdaq exchange was marred by a series of technical problems, rattling investors unsure if their orders to trade went through. In 2013, trading in options in Chicago was halted due to an outage caused by software problems.
The White House says President Barack Obama has been briefed on the technical issue that has halted trading on the New York Stock Exchange.
The New York Stock Exchange says a technical problem that has suspended trading since late morning is an internal technical issue and not the result of a security breach.
The exchange made the statement in a tweet on its official Twitter account. The trading halt is ongoing and has so far lasted about an hour Wednesday.
NYSE-listed stocks are still trading on other exchanges. The Nasdaq and other exchanges are unaffected by the outage.
The New York Stock Exchange stopped trading in the late morning Wednesday because of a technical issue, though shares continued to trade on other exchanges.
The exchange says in a statement that it is experiencing a "technical issue" that it is working to resolve as quickly as possible. It did not specify the exact nature of the technical issue.
Trading continued on Nasdaq and other exchanges.