A project to create a massive market-surveillance database for US financial regulators is encountering fresh resistance from Wall Street brokerages that fear it could be targeted by hackers seeking investors’ private information.

Some of the biggest US brokerage firms are baulking at a contract they must sign to connect their systems to the Consolidated Audit Trail, or CAT, ahead of a deadline just three months away. The brokers have cited concerns that they could be held liable if the database is breached, spurring costly lawsuits, people familiar with the matter said.