Thanks for pointing this out. It is a huge deal and a major problem for all proof-of-work currencies, especially when they have the same pow algorithm as other projects with more hash power. There's been multiple double spend attacks on different networks recently, even zencash fell victim. One more reason why proof of stake and delegated proof of stake algorithms are the future since they provide better security, faster transaction times, and future applications that could never work well on pow. Steem and EOS FTW.