More than a million Americans have been effectively blacklisted from big banks because they overdrew their accounts or bounced a check. Regulators say that the banks are using private databases intended to weed out serial fraudsters to screen out potential customers, swelling the ranks of the unbanked. Next week, New York’s attorney general will become the first government authority to take aim at how banks use the databases when they announce that Capital One has agreed to fundamentally change the way it uses the largest database, ChexSystems. The Consumer Financial Protection Bureau is also monitoring banks' use of the databases.