After Colin Thomas of Miami Beach, Fla., registered his Chevrolet Impala in 2002, his vehicle registration information — along with 284,000 others — was sold by the state to a Coral Gables, Fla., law firm researching litigation against car dealerships.

Thomas sued Charles M. Hartz and his law firm, George Hartz Lundeen Fulmer Johnson, claiming the attorneys violated the federal Driver’s Privacy Protection Act. The law drastically limiting the release of state motor vehicle data was designed to eliminate easy access to private information after the slaying of an actress by a stalker. The Coral Gables firm said it was just trying to build a case against unscrupulous car dealers.