QUITO, Ecuador—Satoshi Nakamoto and Hugo Chávez had at least one thing in common: Both created virtual currencies whose popularity is growing but which are also raising alarms among law-enforcement officials.

Where the pseudonymous Mr. Nakamoto is credited with creating bitcoin, the late Venezuelan president created the sucre, a virtual currency designed to dethrone the dollar as the main trading currency used with his country's regional trading partners: Ecuador, Cuba, Bolivia and Nicaragua.

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