Not all competition prize are fakes, but where there are real competition prize, there will also be scams to exploit the greed.

This is well said:
“Members of the public must
realize that prize-winner announcements that demand the immediate
transfer of money are fraudulent,” head of the investigation division
of the social security and aid directorate general at the Social
Affairs Ministry, Irwan Rais, told The Jakarta Post last Thursday.

“There is no such thing as an obligation to pay prize tax into a bank account owned by an individual,” he said.

In fact, never trust any prize winnings which you did not participate, and always contact the parent company running the competition, game, etc.