Here are five things you need to know about what caused it and the fallout from the lack of trading.

1. Trading on the NYSE was stopped at 11:32 a.m.ET on the stock exchange only. Trades went through on other markets like the NASDAQ and the S&P 500. There had been an earlier computer problem, but it was cleared before the markets opened at 9:30 a.m.ET, Market Watch reported. You can see how abruptly trading stopped thanks to a Twitter post.

At one point during shut down, the Dow Jones briefly dropped more than 200 points, USA Today reported.

2. Hacktivists Anonymous actually posted a comment concerning Wall Street last night at 11:45 p.m.ET, nearly 12 hours before the meltdown.

3. Government law enforcement officials, however, said there was no criminal investigation needed into the glitch about an hour after trading stopped Wednesday. President Barack Obama had been briefed. The Security and Exchange Commission is watching the situation.

4. There have been trading stops in the past because of technical difficulties.

5. During the same time the Wall Street Journal's main site was also down, Time reported. The Dow Jones is the publisher of The Wall Street Journal, owned by Rupert Murdoch's News Corp. The NYSE glitch came a few hours after a computer problem caused a ground stop for all United Airlines flights. Experts have repeatedly said they are not connected.