The Brazilian government released some dramatic pictures of one of South America's last remaining uncontacted indigenous tribes. It says it took the pictures to prove that the tribe existed, because there apparently were some people who doubted this.
When I saw the pictures, I couldn't help but be reminded of the Stone Age Tasaday from the Philippines. The Tasaday were a tribe that was discovered in 1971. Unlike the Brazilian tribe (who are seen shooting arrows at the helicopter taking their picture), the Tasaday were entirely non-violent. They were often called the "Gentle Tasaday." In fact, it was said that they didn't even have a word in their language for "enemy" or "conflict".
But the Tasaday were outed as a hoax in 1986. It was alleged they were actually local farmers who had been paid by the Marcos government to dress up as a Stone Age tribe. Recently, however, the tribe's reputation has been rehabilitated. The consensus among academics now seems to be that the Tasaday were, in most respects, a "real" tribe living in Stone-Age-like conditions.
The problem with calling any tribe "uncontacted" is how you define contact. I doubt there's any tribe in the world that is truly isolated. There's usually some kind of contact (trade, intermarriage, etc.) with neighboring tribes, and so bits and pieces of the modern world find their way to the tribe.