The credit reporting agency Equifax said Thursday that hackers gained access to sensitive personal data — Social Security numbers, birth dates and home addresses — for up to 143 million Americans, a major cybersecurity breach at a firm that serves as one of the three major clearinghouses for Americans’ credit histories. Equifax said the breach began in May and continued until it was discovered in late July. It said hackers exploited a “website application vulnerability” and obtained personal data about British and Canadian consumers as well as Americans. Social Security numbers and birth dates are particularly sensitive data, giving those...