The Nasdaq Stock Market is one of the world's leading stock markets, operating an electronic, screen-based equity market that lists more companies and has more trading activity than any other stock market in the world. In May 2001, HFCP IV invested $240 million to purchase convertible subordinated debentures representing an approximate 15% ownership interest in Nasdaq. With this investment, H&F was the first outside shareholder of Nasdaq interested solely in maximizing the value of the equity and helped Nasdaq transition from a membership-owned organization to a public corporation. In April 2005, HFCP IV entered into a follow-on investment in Nasdaq to support its acquisition of INET, the electronic communication network (ECN) of Instinet. HFCP IV completed the sale of its investment in Nasdaq in December 2007.