OGPU is a secret organization that has operatives around the world. It tends to be involved in terrorists. Despite the fact that the events of Lightning took most of the organization down, it still runs at large.
The basis for the OGPU is the real spy association run in the U.S.S.R., which was named the Cheka before 1921. The OGPU was made famous in the book "The Adventures of Tintin in the Land of the Soviets". Coincidently, the real OGPU worked with bombs when they existed.