Ambush marketing

it is a term often hissed in industry circles – occurs when one brand pays to become an official sponsor of an event (most often athletic) and another competing brand attempts to cleverly connect itself with the event, without paying the sponsorship fee and, more frustratingly, without breaking any laws. Ambush, or guerilla, marketing is as undeniably effective as it is damaging, attracting consumers at the expense of competitors, all the while undermining an event’s integrity and, most importantly, its ability to attract future sponsors.
e.g.2000 Sydney Olympics: Qantas Airlines’ slogan "The Spirit of Australia" sounds strikingly similar to the games’ slogan "Share the Spirit." Qantas claims it’s just a coincidence to the sound of official-sponsor Ansett Air helplessly banging its fists on the conference room table.