The U.S. government, without the knowledge of many banks and their customers, has engaged for years in a secret effort to track terrorist financing by accessing a vast database of confidential information on transfers of money between banks worldwide.

The program, run by the Treasury Department, is considered a potent weapon in the war on terrorism because of its ability to clandestinely monitor financial transactions and map terrorist webs.

Under this effort, Treasury routinely acquires information about bank transfers from the world’s largest financial communication network, which is run by a consortium of financial institutions called the Society for Worldwide Interbank Financial Telecommunication, or SWIFT.

The SWIFT network carries up to 12.7 million messages a day containing instructions on many of the international transfers of money between banks.