Yahoo (YHOO, Tech30) confirmed on Thursday data "associated with at least 500 million user accounts" have been stolen in what may be one of the largest cybersecurity breaches ever. The company said it believes a "state-sponsored actor" was behind the data breach, meaning an individual acting on behalf of a government. The breach is said to have occurred in late 2014. "The account information may have included names, email addresses, telephone numbers, dates of birth, hashed passwords (the vast majority with bcrypt) and, in some cases, encrypted or unencrypted security questions and answers," Yahoo said in a statement.