Security on New York city subways is being scaled back after an intelligence threat of a major attack on the city’s underground transportation system has been discredited. Law enforcement officials told the New York Times that an investigation has yielded no evidence that a plot was in motion or being actively contemplated. From the outset, federal officials have cast doubt on the intelligence that allegedly revealed the threat. New York City Mayor Michael Bloomberg and Police Commissioner Ray Kelly have vigorously defended their decision to go public. Bloomberg has so far refused to release any specific details of the threat. He announced it just hours before he was scheduled to take part in a debate on Thursday with challengers running against him in the upcoming city elections.