Major disruptions caused by Superstorm Sandy led many businesses in the Northeast to reconsider how they build resilience into the data processing and communications portions of their operations.

When Sandy hit, many companies assumed their computer operations would be unaffected because they'd arranged for “hot site” backup facilities, said Joe Stavish, senior vice president and director of property risk control engineering at Willis North America Inc. in New York. A hot site is a duplicate of the main computer system located at an off-site facility to which operations can be transferred in the event of a disaster.

“The philosophy was (backup facilities) shouldn't be in the same building or even across the street, but 20 or 30 miles away should be OK,” Mr. Stavish said. But because Sandy was a regional catastrophe with power and communications disruptions affecting a much wider area, many backup hot sites have been moved hundreds of miles away, he said.

“Vital digital infrastructure — computer-based systems — are different than what we normally think about with bridges,” said David Woods, a professor of integrated systems engineering at Ohio State University in Columbus, Ohio. “We need to think about the fact that so many of our activities are dependent on digital services.”

Mr. Woods was involved in a recent case study examining the computer resilience of a financial sector company where “everything is digitally based,” he said.

The company tested its resilience by taking down data centers in off hours to see if it could restore service. “The problem was they looked at one data center at a time. So (Hurricane Irene) led them to think about "We can have multiple data centers affected by one event,'” he said.

“They discovered that a variety of their plans wouldn't work if they were confronted by a large-scale event that affected more than one data center,” Mr. Woods said.

Sandy's disruption of power and communications also prompted many companies to rethink plans to rely on cellphone communications and employees' ability to work online from home when offices were inaccessible. “Now all the companies are looking at multiple redundancies for Internet communications,” said Mr. Stavish.

For continuity, “we have a lot of conversations with people about whether they wanted to purchase satellite phones or whether they wanted to purchase individual power packs for certain executives,” said Tracy Knippenburg Gillis, reputational risk and crisis management leader for Marsh Risk Consulting in New York.