At 11:32 am on Wednesday, the NYSE stopped trading.
As yet, no one knows why. The NYSE has said that's it's not a hack though.
"The issue we are experiencing is an internal technical issue and is not the result of a cyber breach," the 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."
Software experts tell Business Insider that this could be a problem with NYSE's stock pricing program, similar to what happened at the NASDQ in August 2013.
Additionally, Eric Hunsader, CEO of market research firm Nanex, says that these things can happen when a software system's update goes wrong.
He tweeted out this chart of what it looked like in the world of exchanges when everything went south.
As this chart shows, the NYSE started out low at 9:30. At 10:45 things went down hill: pic.twitter.com/qLnk1TduDJ
- Eric Scott Hunsader (@nanexllc) July 8, 2015Contrast that with what exchanges look like on a normal day, like Tuesday.
For reference, this was the trading breakdown by reporting exchange for yesterday: pic.twitter.com/ZK6xUpJrqI
- Eric Scott Hunsader (@nanexllc) July 8, 2015