A major derivatives trader, CME Group, had admitted it fell victim to a security breach in July, which leaked information on some customers.

CME, described by Bloomberg as the world’s largest futures trader, said in a statement that “to date” there was no evidence that the unknown attackers had affected trades on CME Globex, or that trading in its markets was disrupted, according to a report by PC World.

The Chicago based firm runs four exchanges, according to PC World, and said in its statement that it was corresponding “directly” with affected customers.

The company said that the “cyber intrusion” had happened in July, and said in a statement that it was “one of the many organizations subject to this type of crime in recent months.”

Bloomberg described the electronic attack as a reminder of “one of the most constant threats” to financial services firms.

Bloomberg pointed out in its report that firms such as JP Morgan and Citigroup had also fallen victim, and quoted Craig Pirrong, a finance professor at the University of Houston,  “We shouldn’t view this as a futures market story alone, all financial services and markets are a target. Investors do need to be concerned.”

The company said that its security teams took “prompt” and “significant” action, saying, “To protect participants, CME Group forced a change to customer credentials impacted by the incident, and is corresponding directly with the impacted customers.”

The attack is the subject of an “ongoing federal criminal investigation”, the company says. CME says it is cooperating with law enforcement.