Recently only, a guy hacked Ola Cabs Wallet ( A competitor to Uber in India) by exploiting their REST API [1].

A similar post on race condition of Facebook, Digital Ocean was discussed here in HN [2]

[1] https://medium.com/@CodeTheDevil/busting-ola-wallet-1ceea617... [2] https://news.ycombinator.com/item?id=9443867