Mary Jo White, the chair of the U.S. Securities and Exchange Commission, said in a speech Friday that cyber-attacks against the U.S. are the “biggest risk we face.”On the same day, USA Today reported that John Carlin, the head of the Justice Department’s National Security Division, said at a hedge-fund conference that several firms had been victimized by “cyber-extortionists.”Still, one law firm’s survey discovered that the biggest cause of data-security problems is human error.