If al Qaeda had a sense of humour
but the real danger is that al Qaeda might mischievously spoof the program...
There are already rumours of people receiving unsolicited al Qaeda spam (and I don't just mean the secret codes apparently included in Viagra spam (those NSA guys are good, I thought that spam had no information content at all...). This of course is bad, because it might make innocent people, like say liberal politicians or academics, suspects that the NSA feels should be monitored. And that would just be wrong and unAmerican.
But, al Qaeda could really wreak havok if they started doing mean pranks, like phoning former Coalition Provisional Authority employees, using cell phones known to be compromised, and leaving cryptic messages on answering machines - like "the game is afoot" or "confirming: pizza with ham AND pineapple?". If answered in person they could utter fake identification codes, like "shame Seattle lost" or "should have been the Colts", interspersed with "you don't think they're monitoring your phone, do you?"
I mean, clearly one of the groups most likely to be infiltrated by 5th columnists are CPA employees who went "native", or were bribed, and it would be very confounding if al Qaeda were to divert suspicion to many innocent hard working patriotic citizens in order to obscure their true activities.
Fortunately, it is very clear that al Qaeda does not have a sense of humour.