A pair of hacking bombshells that exposed personal information stored in more than 1 billion Yahoo user accounts, disclosed after Verizon and Yahoo had agreed on takeover deal, represent the two biggest security breaches in internet history. a Yahoo is taking a $350 million US hit on its previously announced $4.8 billion US sale to Verizon in a concession for security lapses that exposed personal information stored in more than 1 billion Yahoo user accounts.