They can then spend the electronic currency on multiplayer games, casual games, and virtual worlds.

FORBES: Connect

Liberty Reserve, which conducted its transactions in dollars, euros and rubles, operates as an anonymous, no-questions-asked alternative to the global banking system, said Aditya Sood, a computer science doctoral candidate at Michigan State University who has studied the electronic currency.

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People trying to profit via the bitcoin electronic currency will soon have to work harder to mint the digital coins.

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Liberty Reserve's origins are obscure, but it had grown into one of the criminal underworld's best known electronic currency systems, used by hackers the world over to discreetly move large sums of money across borders, experts say.

WSJ: Costa Rica: Digital currency site founder arrested

Currently, transactions within the shadow economy have to be made face to face, but an electronic System D currency would enable remote and even cross-border transactions.

FORBES: Could Bitcoin Become the Currency of System D?