Over the past weekend, on block 11380000, a solution for the prevention of 51% attacks was introduced to the Ethereum Classic (ETC) community. Several such attacks have recently placed ETC at a crossroads, leaving the very survival of the chain uncertain. In the weeks that followed these attacks, the community worked to evaluate numerous potential solutions.
The first one that has been implemented is called MESS, which stands for Modified Exponential Subjective Scoring. Its predecessor was first suggested by Vitalik Buterin back in 2014. It builds on the assumption that while small chain reorganizations that go back a few blocks are perfectly normal, the ones proposing reorganizations going back hundreds and even thousands of blocks are highly suspicious.