Markit, a little-known but critically important firm that provides derivatives pricing and index products, is the focus of a Justice Department antitrust investigation, according to several news reports.

Markit shareholders include many of the world's largest financial institutions, including Goldman Sachs ( GS), Morgan Stanley ( MS), JPMorgan Chase ( JPM) and Citigroup ( C). The Justice Department probe is reportedly focusing on whether banks give Markit unfair access to pricing information, providing an edge over potential competitors, according to Bloomberg.

Markit's index products are widely used to create derivatives, and a series of indices Markit created in 2006 known as the ABX allowed hedge funds and other market participants to make large leveraged bets against the subprime mortgage market. Some say these indices provided the fuse that allowed traders to blow up the global economy.

Markit was set to release its first series of indices tied to prime mortgages in December, but postponed the launch the day after reported on the pending launch and raised questions about the effect it might have on fragile markets.