Elon Musk briefly worked illegally in the US after abandoning a graduate studies program in California, according to a Washington Post report that contrasted the episode with the South African multibillionaire's anti-immigration views. But the Washington Post reported Saturday that the world's wealthiest individual was almost certainly working in the US without correct authorization for a period in 1995 after he dropped out of Stanford University to work on his debut company, Zip2, which sold for about $300m four years later.