NYC Subways Targeted?

So the word is the FBI have passed on some pretty reliable information to the NYPD in regards to NYC being the target of another terrorist attack. Security on subways and transit in general has been upgraded and there is a show of force by multiple agencies. Washington has stated that the information has not proven "reliable".

So is there info, or isn't there? The Mayor seems to think it's better that we are informed about a "possible" threat, and acknowledges that the information is pretty specific to date, place, time etc. If that's the case then why tell us at all. Wouldn't it have been smarter to get the agencies involved prepared and then spring the trap when all the targets present themselves? Now, if there really is a threat, won't they cancel, postpone, or move to another location? That doesn't make much sense at all....Unless this is simply a bluff to keep the terrorists guessing? Maybe we know that 19 terrorists are in NY planning an attack, but we have no idea where, when or how and this ruse is for their benefit. If they think we're coming for them, they won't attack...Yet. Don't know, but if it's true, I hope we catch these bastards and we catch em before anyone gets hurt.