Since Russia annexed Crimea in 2014, American companies have been prohibited from dealing with MMZ Avangard, a state-owned firm that makes missiles for one of Russia's most sophisticated weapons, the S-400 air-defense system. But even as the United States was taking actions to blunt MMZ Avangard's business, a publicly traded American technology company, Extreme Networks, was providing MMZ Avangard with computer networking equipment for its office IT systems.
