Following on the heels of an embarrassing security lapse by McAfee and its accounting firm Deloitte & Touche, financial giant Ernst & Young acknowledged Friday that it, too, had lost sensitive data that could be exploited by identity thieves. In a letter dated Feb. 13, Ernst & Young warned clients that their Social Security numbers were on a laptop that was stolen from an employee’s locked car. Santa Clara antivirus softwaremaker McAfee warned 9,000 current and former employees in a letter dated Feb. 17 that a compact disc containing their names and Social Security numbers was lost.