The New York Stock Exchange just explained why trading was halted for 3 hours on Wednesday

A software release caused the blackout at the New York Stock Exchange on Wednesday.

According to an update on the NYSE's website on Thursday, the exchange started rolling out a software release ahead of a scheduled industry test on Saturday.

A software release caused the glitch.

It noted that gateways for customers were updated with the right software at the market open on Wednesday.

But issues with the software cropped up later in the morning, prompting the NYSE to suspend trading.

The "market status history" update on the NYSE's site posted Thursday said: "As customers began connecting after 7 a.m. on Wednesday morning, there were communication issues between customer gateways and the trading unit with the new release.

 It was determined that the NYSE and NYSE MKT customer gateways were not loaded with the proper configuration compatible with the new release."

Trading was halted at the exchange for more than three hours, though listed stocks still changed hands through other venues and exchanges.

The NYSE had stressed that the halt was not because of a cyberattack.

Read the full release below:

On Tuesday evening, the NYSE began the rollout of a software release in preparation for the July 11 industry test of the upcoming SIP timestamp requirement. As is standard NYSE practice, the initial release was deployed on one trading unit. As customers began connecting after 7am on Wednesday morning, there were communication issues between customer gateways and the trading unit with the new release. It was determined that the NYSE and NYSE MKT customer gateways were not loaded with the proper configuration compatible with the new release.

Prior to the market open, gateways were updated with the correct version of software and stocks opened at 9:30am. However, the update to the gateways caused additional communication issues between the gateways and trading units, which began to manifest themselves mid-morning. At 11:09am, NYSE issued a Market Status message that a technical issue was being investigated. At 11:32am, because NYSE and NYSE MKT were actively trading but customers were still reporting unusual system behavior, the decision was made to suspend trading on NYSE and NYSE MKT. NYSE ARCA, Arca Options and NYSE AMEX Options were not impacted by this event and continued to trade normally.

NYSE and NYSE MKT began the process of canceling all open orders, working with customers to reconcile orders and trades, restarting all customer gateways and failing over to back-up trading units located in our Mahwah, NJ datacenter so trading could be resumed in a normal state. In consultation with regulators and industry, we determined that we would implement a complete restart and that NYSE MKT primary listings would resume trading at 3:05pm and NYSE primary listings and NYSE MKT Tape C symbols would resume trading at 3:10pm. Trading resumed as scheduled and the closing auctions accepted orders and executed normally. All NYSE and NYSE-MKT listed securities traded for the entire day either on NYSE and NYSE MKT or other market centers.