In the world of IT, we often rely on the fact that the real world claimant of any information who must then be authenticated, before he may be permitted the use of his information, will also possess and may timely share certain secrets unknown to anyone else.

ECONOMIST: Fake ID cards

The exact mechanism is unknown, but certain bacteria are thought to facilitate important interactions between the gut and the brain.

WSJ: A Gut Check for Many Ailments

"The sell-off is a step into the unknown in that we cannot be certain that it would provide service equal to that provided by the RAF, " said Mr Jones.

BBC: Helicopter search and rescue for Caernarfon, St Athan

Punters pay for tickets to see an unnamed film at an unknown location with instructions to dress to a certain theme.

BBC: Cinetastic Melbourne

With each early stroke, with each pitch and roll, I felt certain I would upset its delicate balance and topple into the unknown dangers lurking beneath.

BBC: Safari by water in southern Africa

Ever get a text message from an unknown number that asked if you were interested in a certain service?

FORBES: How To Get Phone Bill Crammers To Scram

And this surmise is made absolutely certain, in the view of the managers, because a newly discovered, unknown even to the independent counsel, cell phone record shows that Ms. Currie called Ms. Lewinsky at 3:32 p.m. on December 28, and that must be the call that Ms. Lewinsky remembered.

CNN: Transcript: White House Counsel Ruff's opening statement