The first known usage of the term ‘spyware’, as far as I am aware, was back in October of 1994.
On the 17th of that month the phrase cropped up in a posting made on Usenet, a globally distributed bulletin board system.
Several years later, in 2000, Steve Gibson, owner of Gibson Research (a computer software development firm), discovered that advertising software components from two companies had been installed onto his system and he suspected them of collecting information without his knowledge.
Later on he would retract that claim but he still reprimanded the advertising companies Aureate and Conducent for secretly installing spyware and giving him a hard time to remove it.
This event led to Gibson creating and releasing ‘OptOut’, which was the first known antispyware program.
Since that time many other security vendors have followed suit and created ever more complex solutions to the increasing problem of spyware.
Spyware is currently estimated to be on anywhere between 80% and 90% of all computers, generally without the owner having a clue of their existence or presence.
Typically, machines running Microsoft Windows operating systems and/or the Internet Explorer browser appear to be more at risk due to the popularity of those products.