It's my understanding that 'spies' in the ancient world would generally be people who were bribed or coerced into working for a hostile power on the side, as opposed to people who collected sensitive information for a living. Today, however, 'spy' has a similar connotation to 'foreign operative'. When did this change occur?
While field agents exist today, by and large the perception you're thinking of can most be credited to movies and fiction. Especially with the interest of the Cold War coinciding with the rise of cinema, the American public was saturated with spy novels and films, such as James Bond or Tom Clancy's work.
But the most common modern usage of spies is precisely what you described.
For instance, relatively recently (2011) there was a massive breach of American spies in Lebanon. The spies in question were Lebanese nationals coerced into working with American Intelligence and typically speaking, this remains the most common form of "spy" on the ground.
The suave, gun toting super spy or the gadget laden lone warrior of Ian Fleming or Tom Clancey are equal parts myth, exaggeration, and rarity.