A representative of CSC did not respond to a request for comment on the report.

More than half of the 20 largest auto and property insurance companies in the U.S. use CSC's Colossus, and many others use similar products from competitors, Hunter said. The claims software market is largely unregulated by state insurance agencies, and "I'm convinced there are millions of Americans still at risk," he said.

CSC originally marketed Colossus as a cost-savings product, but shifted to talking about the software as a way for insurance companies to achieve consistency in claims payouts, the report said. Some insurance companies were uncomfortable with the software marketing as a money-saving package, said the report, referencing CSC materials made public against the software vendor settled in 2009.

"Consistency, in and of itself, is a legitimate goal," Romano said. "However, insurers aren't investing millions of dollars in this software just to achieve consistency. They're looking to save millions more by underpaying injury claims."

Insurance companies can tweak Colossus and similar software packages in several ways to lower claims payouts, the report said. Insurance companies can use the software to reduce payments by a predetermined percentage, and they can exclude high-cost claims from original tuning results used to determine the costs of injuries, the report said.