A system and method are described and disclosed that are used for effecting large block trades of securities in an automated and anonymous matter in which fair pricing is carried out using features of the National Best Buy Offer (“NBBO”). The automated trading the system and method also will carry out negotiations to effect a trade in certain circumstances, though the preferred method of effecting trades is by automated trading. However, regardless of the trading method, anonymity of the trading counterparties is preserved. The system and method also tests the NBBO for each of the traded securities to ensure it is valid before an automated trade may take place.