Hacking contests, which are common, are a way to reduce the number of hires by posting difficult questions their teams should handle out into the public.
The total of prizes is cheaper than hiring a team that may or may not be able to find problems either. [almost 100% of contest participants will fail].
People will be working for Google for free and of the many thousands of people that will do the work, only three will get paid anything.
The winners are rewarded well, a year or more salary for a single task.
Everybody else gets nothing but the satisfaction of trying. The same business model is followed in design companies. “Spec work” it’s called.
But if you’re up for the challenge and don’t mind the richest media company on the planet earth doing this, here’s the information.
Additionally, for more information on “Spec work” and why it’s unethical here’s: