Global payment companies held their first joint cybersecurity war games to test their systems' readiness for simultaneous attacks, uncovering differences in their defenses including even how to define a crisis.

JPMorgan Chase & Co., Mastercard Inc., American Express Co., WorldPay Inc., and Fidelity National Information Services Inc. were among the 18 payment processors from the U.S. and the U.K. that took part in the exercises, which were held Friday at IBM's test center in Cambridge, Massachusetts. Some of the findings, which will be disclosed at a conference in Atlanta Wednesday, were shared with Bloomberg News in advance.

Financial firms have led spending on cybersecurity as high-profile attacks exposing customer data and theft of funds raised pressure on the industry. Executives and regulators are concerned that a systemic attack on the plumbing of the financial system could disrupt the global economy, and cooperation between the industry and government agencies is increasing.