Six years ago, when North Vally Bank began selling its excess data processing capacity to three other small California banks, chief executive Donald Carter thought he had found a good thing.

"We just wanted to cut our costs," Mr. Carter said.

Limited Time Offer

Save $400 off your subscription. Special offer ends April 30, 2017.

14-Day Free Trial

No credit card required. Complete access to articles, breaking news and industry data.