MAGNITOGORSK, Russia (Reuters) - Unknown hackers stole 339.5 million roubles ($6 million) from a Russian bank last year in an attack using the SWIFT international payments messaging system, the Russian central bank said on Friday. The disclosure, buried at the bottom of a central bank report on digital thefts in the Russian banking sector, is the latest in a string of attempted and successful cyber heists using fraudulent wire-transfer requests. The central bank said it had been sent...