We, the general public, don't know what secrets the security agencies have locked in their vaults, the threats they have identified or the plotters they might be monitoring.

But we know one thing. This system of grading the terrorist threat is a cheap gimmick, plain and simple.

US President Barack Obama vows to target ISIL. Credit:AFP

The public is no better informed or protected by raising the arbitrary "National Terrorism Public Alert System" from a rating of medium to high.

The only consequence will be an initial burst of panic and unfair suspicion.