It's a possibility that no-one is prepared to discuss, and it's a scenario that could quite simply destroy what little confidence there is left in our financial markets.
But speculation is mounting in some quarters that a specialist Al-Qaeda cell was behind the 1,000 point drop in the Dow Thursday, which spooked the markets, and unnerved financial professionals around the world.
The terrorist angle, of course, is just one theory which, given there has still been no official explanation for the market plunge and subsequent partial pullback, is doing the rounds.
Some blame an unfortunate systems error that caused price distortions between various exchanges, others claim that it was automated trading programs that fed on themselves to cause a downward price spiral, yet more think that it was panic sellers concerned about an overdue market correction prompted by fears of Greek contagion, and there are even those who believe it was a massive conspiracy by bankers to exploit price movements for their own evil purposes. Not to forget the 'fat-finger' trader theory. Then there are groups of people who think that all, or a combination of, the above were to blame!
But some market participants are starting to think the unthinkable. One security analyst told Here Is The City: 'No-one should underestimate Al-Qaeda. 9/11 was a highly organised affair, and don't forget that it was primarily designed to destabilise the financial markets. Bin Laden is aware that he can't defeat the forces aligned against him in a face-to-face pitched battle, but he can wage a clever war that hits the developed world where it hurts - in its pocket'.
The analyst continued: 'Although I certainly have no knowledge about a specific plot, it is quite conceivable that Al-Qaeda, or another terrorist group with similar goals, may have somehow hacked into the exchange systems (or even had people there on the inside). And the ideal time to have caused maximum panic was last Thursday - when the markets were already nervous about Greek and other European country debt, and the British were well on their way to an inconclusive Election result'.
One trader told Here Is The City: 'The longer the authorities take to come up with a plausible reason behind Thursday's incredible events, the more likely that off-base theories like those involving a terrorist link will gain currency. And this will do nothing to stem the tide of panic both in the markets and on the ground, especially in the wake of The Times Square bombing attempt a few days back'.
Such is our current total distrust of government and all things 'official', however, that even a denial by the authorities that terrorists were behind Thursday's market plunge will cut no ice with many.