Charlie Lee, the creator of Litecoin (LTC), tweeted on 7 January 2019 that a cryptocurrency must be susceptible to a 51% attack, no matter by hash rate, stake or other resources which could be obtained without a third party’s permission, to be defined as decentralized.

The tweet was made in response to another tweet by user CryptoTesla, which stated that “if it can’t be 51% attacked, it isn’t decentralized”. The stated tweets were made as a response to an announcement made by Coinbase, a major crypto exchange. The announcement, made on the same day, stated that the platform detected “chain reorganizations” and double spends on Ethereum Classic’s (ETC) blockchain.

The unusual mining activities were said to be a 51% attack, a hypothetical attack made on blockchains by a group of miners who control more than 50% of hash rate or computing power of the whole network. From 5 January 2019, Coinbase suspended deposits and withdrawals of the cryptocurrency and the suspension is still currently in place. On 8 January 2019, the platform updated that 12 additional chain reorganizations occurred which included double spends surmounting to 219,500 ETC (approx. $1.1 million).

However, developers of the cryptocurrency denied allegations that the activities were a 51% attack. They claimed that double spends never happened and the suspicious mining was most probably just “selfish mining”. They also suspected that testing of new Ethash machines developed by ASIC (application-specific integrated circuit) manufacturer Linzhi which promised 1,400 Mh/s hash rates may contribute to the digital currency’s increased hash rate. The manufacturer denied the claims in a deleted tweet.

The issue also led to discussions of whether certain cryptocurrencies are considered decentralized. Some users stated that Ripple’s (XRP) structure made the currency invulnerable to double-spend attacks. Additionally, the creator of the currency, Ripple, holds most of the circulating XRP, thus the currency cannot be defined to be decentralized.

On the other hand, some users claim that Bitcoin (BTC) and other digital currencies which utilise Proof-of-Work in their algorithm could not be considered decentralized since the currency since the majority of mining activities occur in China and the government’s decisions could affect the currencies’ operations.