A mistake by an employee who forgot to turn off the system affected the stocks of more than 250 companies and led to the cancellation of thousands of trades on the New York Stock Exchange (NYSE) last Tuesday, 24. The problem, oddly enough, occurred in the disaster recovery system.

The New York Stock Exchange’s data backup center is located in Chicago, more than 1,100 kilometers from its physical headquarters, and does the chores of turning systems on and off just after markets close to make sure everything works.

However, on Monday, the 23rd, an official forgot to properly shut down the disaster recovery system, causing the exchange’s computers to misinterpret Tuesday’s 9:30 am open as a continuation of the previous day’s trading.

At the same time, computers skipped the opening auctions of the day, which set the starting prices. Without a stage, there were offers with a variety of prices.

Mechanisms designed to prevent wild market fluctuations eventually activated and triggered alarms on the trading table screens. Shares of companies such as AT&T, Verizon and Morgan Stanley suffered. In some cases, fluctuations of 25 percentage points were observed in a matter of minutes.

Trading in several shares had to be temporarily suspended shortly after the opening of trading hours, and then they were canceled.

The NYSE said in a statement that the opening auction for some stocks was not held due to a “systemic issue.” A number of transactions took place before price caps were set. Under current rules, these transactions are subject to review by the exchange operator, who may classify them as “manifestly erroneous”.

In this scenario, the NYSE chose to void trades that occurred after the 11:30 AM (Brazil time) open but before the upper and lower limits were determined. He also evaluates the classification of transactions as abnormal. “This action will exclude these executions from the calculation of the high or low price of the day,” the note emphasizes.

The cost of the chaos created is still being calculated. Market professionals and amateur traders are shocked and hope the exchange will explain what it has publicly described as a “manual error” related to its “disaster recovery setup”.

The Securities and Exchange Commission (SEC, American Securities Commission) told Estadão/Broadcast that the regulator’s technical team is studying the activity and is in direct contact with the exchange. The official who allegedly made the mistake has not yet been identified.