illegal dumping; fly-tipping
tort; illegal act; illegal activity; offence; offense
illegal entry (into a country); illegal immigration
illegal residence (in a country); illegal stay; illegal overstaying (of a visa)
illegal immigration; illegal immigrant
illegal possession; unlawful possession
illegal employment; illegal work; unauthorized labor
unlawful occupant (e.g. of a house, apartment, etc.); squatter
unlawful detention (of shipping); unlawful occupation (of a house or land)
unlawful occupation (e.g. of a house, of land, etc.); squatting
(illegally) overstaying one's visa
illegal acquisition; unlawful appropriation