United States v. Microsoft Corporation is a U.S. antitrust law case, ultimately settled by the Department of Justice, where Microsoft Corporation was accused of becoming a monopoly and engaging in abusive practices contrary to the Sherman Antitrust Act 1890 sections 1 and 2. It was initiated on May 18, 1998 by the United States Department of Justice (DOJ) and 20 states. Joel I. Klein was the lead prosecutor.