I've encountered this expression on the book "UNIX: A History and a Memoir".
One day I was scheduled to do a demo for William Colby, who at the time was the director of the Central Intelligence Agency (CIA), and thus clearly an important person. He too would be accompanied by Bill Baker, who as head of the President’s Foreign Intelligence Advisory Board had serious spook credentials of his own.
I searched it on the web and got some results from English websites, but no proper explanation anywhere. There wasn't any usage on my local language web sites.
Could someone explain the meaning and general usage of the expression?