A Chicago-based company that runs derivatives exchanges was the victim of a July cyberattack that compromised customer information.
CME Group, which runs four exchanges, said that information belonging to customers using its CME ClearPort services for the OTC market was compromised. ClearPort is a centralised clearing service for energy markets, according to the company's website.
"To protect participants, CME Group forced a change to customer credentials impacted by the incident, and is corresponding directly with the impacted customers," the company said.
The intrusion is under investigation by federal law enforcement, CME Group said. It did not explain why it was disclosing the attack four months later.
Trades using its CME Globex electronic trading platform are not believed to have been affected, and there's no evidence that CME Clearing, CME Clearing Europe and trading in CME markets were disrupted.
"CME Group takes these events very seriously and places a high priority on protecting its customers' information and ensuring the integrity of its markets," it said.
CME Group's exchanges encompass a wide range of trading, including futures, equity indexes, foreign exchange, energy, metals and real estate.