WASHINGTON (Reuters) - Homeland Security Secretary Janet Napolitano warned on Thursday that a major cyber attack is a looming threat and could have the same sort of impact as last year's Superstorm Sandy, which knocked out electricity in a large swathe of the Northeast. Napolitano said a "cyber 9/11" could happen "imminently" and that critical infrastructure - including water, electricity and gas - was very vulnerable to such a strike. A cyber security bill failed in Congress last year after business and privacy groups opposed it. The measure would have increased information-sharing between private companies and U.S. intelligence agencies and...