A logic bomb essentially makes a program switch to a different mode after running several million cycles (changing its "logic"). The pipeline software's logic bomb was set to go off after 10 million cycles. The KGB thieves weren't stupid -- they checked the stuff they were stealing -- but since the software appeared to be working fine, they brought it back to a pipeline in Siberia that extended into Western Europe, singing songs of their good fortune.
The program ran fine for a few months (the aforementioned 10 million cycles), but after that, it took the pipeline's pumps and compressors aside and told them, "Today is the day that we run a pressure test at dangerously high levels." After careful calculations, the CIA expected the pipeline to merely spring leaks all the way across Siberia. Clearly, they overestimated Soviet engineering.
"In Soviet Russia, pipes leak on YOU -- because of CIA meddling. Seriously."
In June 1982, American early warning satellites detected an extremely large blast in Siberia as the pipeline motherfucking exploded. The blast was 3 kilotons, or roughly one-fifth of the strength of the atomic bomb dropped on Hiroshima. It was "the most monumental non-nuclear explosion and fire ever seen from space," a phrase that here means "the most brain-shittingly awesome spectacle ever witnessed by the endless folds of the universe."