Who remembers the Aesop fable about the boy who cried wolf? The moral of that old story still applies, even in these modern times when the boy is likely to cry something that sounds more impressive, such as that he is "picking up increasing levels of wolf chatter."
An example is today's highly publicized warning from the FBI and DHS regarding the Annapolis Peace Conference. They want local law enforcement agencies to know they have no credible information that “extremist organizations” based in Maryland have targeted the Annapolis Peace Conference or nearby Islamic or Jewish sites for disruption or a terrorist attack,“[n]onetheless, DHS does not discount the threat of the lone-wolf terrorists, including individuals radicalized by homegrown extremist groups or Internet content.” A spokeswoman adds that the FBI and DHS “have no intelligence reports indicating a possible threat to the Annapolis Peace Conference (APC); nevertheless, with the media coverage and the sensitive issues involved, the possibility of a terrorist attack against such a prominent event remains.”
I love that adverbial hedging of bets: "nonetheless" and "nevertheless." They have nothing to warn about, but they want to warn you anyway just because, well, you can never tell what might happen. Of course, there is an obvious bureaucratic purpose to these non-assessment assessments. If there is any possibility, however slight, that the FBI and DHS might one day be criticized for their failure to produce an actually useful threat assessment, then they need to cover their corporate asses by pointing to an all-purpose 'hey, anything could happen in this crazy world' type of warning.
These non-warning warnings do more harm than good, in my opinion, considering that the FBI and DHS routinely issue them before all major events and for all significant anniversaries and national occasions. They have become the Hallmark cards of the security world, just as inane and omnipresent, but without the pretty pictures. The cumulative effect of all these pointless warnings is to discredit the whole idea of threat advisories. If you have nothing to warn about, it would be better to remain silent until you do.
As Aesop could have told them, the agency that makes a habit of crying wolf is not believed even on that rare occasion when it happens to be telling the truth.