Beginning in the 1970's, more stringent regulations and scandals, often cyclic events, resulted in a combination of increased transparency and some limitations on exchanges' flexibility as businesses, designed to gently remind the exchanges of their regulatory responsibilities. Yet, these strongholds were not truly challenged until new competitors, primarily ECNs, entered the arena. Thus, despite the significant evolution of the exchange business model over the last century, the regulatory structure continued and continues to be the model of self-regulation although designed for the original, utility-like, exchange model.