One of the world’s largest providers of marketing email services, Epsilon, has warned its clients that they were exposed to what may have been the largest private information breach in U.S. history. Clients of Epsilon include JPMorgan Chase, U.S. Bancorp, Citigroup, Capital One, Barclays Bank, Best Buy, TiVo, Walgreens, Brookstone and the New York Times. Epsilon says a computer hacker infiltrated the company and seized private information — mostly names and email addresses — of customers of their clients. Millions of students may have also been affected. One of Epsilon’s other clients is the College Board, which administers SAT tests.