New York City’s underground system is facing its most specific threat of a terrorist attack ever, it has been revealed.Security has been stepped up on the subway with passengers’ bags being searched and sniffer dogs deployed. City Mayor, Michael Bloomberg, told a press briefing: “The FBI has recently shared with us a specific threat to our subway system. I wanted to assure New Yorkers we have done and will continue to do everything we can to protect this country.” The subway carries between 4.5 and 7 million passengers a day. Many admitted the news of a threat made them feel nervous, despite the highly visible police presence. The alert came as US President, George W Bush claimed 10 al Qaeda plots had been foiled by American intelligence services. The White House, which is playing down the New York threat, later issued a list of the plots.