This excerpt taken from the NDAQ 8-K filed Nov 8, 2007.
Delaware Business Combination Statute
Nasdaq is organized under Delaware law. Delaware law generally prohibits a publicly-held or widely-held corporation from engaging in a business combination with an interested stockholder for three years after the stockholder becomes an interested stockholder. An interested stockholder is a person who, together with affiliates and associates, owns (or, in some cases, within three years, did own) directly or indirectly 15% or more of the corporations outstanding voting stock. A business combination includes a merger, asset sale or other transaction that results in a financial benefit to the interested stockholder. However, Delaware law does not prohibit these business combinations if: