If someone or something enters an area where you would not expect them to be, or where they have not been found before, you can call this an incursion, especially when you disapprove of their presence. her disastrous incursion into the property market
A running into; hence, an entering into a territory with hostile intention; a temporary invasion; a predatory or harassing inroad; a raid
the act of entering some territory or domain (often in large numbers); "the incursion of television into the American livingroom" the mistake of incurring liability or blame