Ethereum Block Chains “Hacked”

An open block revealing digital coins within

The February issue of MIT Technology Review reviews a 51% attack on Ethereum Classic. The article also covers similar attacks on lower value crypto currencies and its progress to now attacking top 20 currencies. Also covered (again) are the current issues with Smart Contracts.
These issues represent the Damocles sword of Crypto Currencies, the openness of its approach is also its biggest weakness.