At FOX website, they have the AP report regarding the threat...in part, it states:
Boston on Alert for Four Terror Suspects
A federal law enforcement official, speaking on condition of anonymity because the matter remains under investigation, told The Associated Press that the FBI's joint terrorism task force has not yet corroborated a tip that the suspects entered the United States through Mexico in recent days, possibly bound for Boston.
I'm having a hard time thinking AQ jobbed this out to some Chinese/ N. Korean loonies. Why would the perps do this, unless of course it's for money and they're not about to be homicide bombers. If they're not in it for ideological reasons, maybe they'd be more inclined to give up if the Feds are on their trail.