Experian PLC said a data breach may have compromised the personal information of roughly 15 million consumers in the U.S., including those who had applied for T-Mobile US Inc. subscription services or devices over two years through Sept. 16. "Obviously I am incredibly angry about this data breach, and we will institute a thorough review of our relationship with Experian," T-Mobile Chief Executive John Legere said in an open letter posted on the company's website. "This is no small issue for us."