A Texas man admitted Wednesday in federal court in New York that he acted as a secret agent for the Russian government and headed an operation over about 10 years to export military technology to that country. Alexander Fishenko, a naturalized U.S. citizen and owner of Houston-based Arc Electronics Inc., pleaded guilty in U.S. District Court in Brooklyn to numerous crimes, including money laundering, obstruction of justice and acting as an agent of the Russian government in the United States. A sentencing date hasn’t been set. Prosecutors say he headed a scheme to purposely evade strict export controls for cutting-edge...