It's a dirty little secret that everyone knows: Bitcoin exchanges built on top of first-generation NoSQL infrastructure lack even the most basic measures to guarantee the integrity of their accounts.
A very interesting article on some Bitcoin exchanges that, based on NoSQL technologies (specifically MongoDB), have suffered from concurrency in their systems and have been (successfully) hacked.
What happened at Flexcoin, or Poloniex, or any of the other Bitcoin exchanges beset by technical problems (and I'm looking at you Coinbase!), was not an outlier or unexpected or unforeseable. The infrastructure is broken. And it is broken by design.
Flexicoin recently suffered a hacker attack that may well be shown to students on concurrency classes so they gain interest on how to make easy money due to exploiting other people's failures.
Bitcoin meets NoSQL: The story of Flexicoin and Poloniex
This article provides some ideas on fixing the problem, and also had the merit, in my case, to introduce HyperDex, a system I didn't know that provides consistency + scalability that they proactively evangelise.
I am working now for a firm specialized in finance, so I'm going to pay an extra attention to this kind of articles.
Extra Ball from Hacking Distributed: How-to make documentation on infrastructure.
