The New York Stock Exchange is open after a 3-hour halt.

At 11:32 a.m. ET on Wednesday, trading on the exchange was halted after a technical glitch.

"The issue we are experiencing is an internal technical issue and is not the result of a cyber breach," NYSE tweeted out about an hour after the halt. "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."

According to Bloomberg, Homeland Security said there is no evidence of a hacking attack.

"So far this is the worst I've seen since the NASDAQ blackout," Eric Hunsader, CEO of market research firm Nanex, told Business Insider.

He added that sometimes these glitches happen when a software update goes wrong.

CNBC's Carl Quintanilla tweeted that this was what NYSE traders saw on their screens right after the halt.

Lev Lesokhin, of software analytics firm CAST agreed with Hunsader that the NYSE outage looked very familiar.

"It seems to be like what happened to NASDAQ when its Securities Information Program (SIP) went down in August 2013," he said.

The SIP handles on the price data for stock exchanges. When it went down at the NASDAQ, it was due to a massive fluctuations of trading volume.

"It's kind of like a denial of service request," Lesokhin explained. Hackers do the same thing when they try to take down a website on the internet — they confuse it by using bots to overload it with information.

Hunsader tweeted the following image, showing that trades from the NYSE dropped, sputtered, and then eventually stopped.

The NYSE first started showing signs of strain at 10:32 this morning, but said the technical issue had been resolved. Then, once it started failing an hour later, it flailed in and out of connectivity before going out entirely.

Stocks are lower in trading, with the S&P 500 and Nasdaq down more than 1%. All sectors of the S&P 500 fell into the red for the day.

NYSE stocks traded during the halt, but were re-rerouted through other venues including dark pools, Bloomberg reported.

SEC Chair Mary Jo White said that her agency is on this.

"We are in contact with the NYSE and are closely monitoring the situation and trading in NYSE-listed stocks. While the NYSE is working to resolve the situation NYSE and NYSE Market stocks continue to trade normally through other venues," she said in a statement.

President Obama and the Treasury have also said that they are watching what's going down.

"We have our best and smartest on the issue and hope that it is resolved ASAP," wrote NYSE floor governor Rich Barry in an afternoon note.