"Mock ad banners will give it the appearance of a commercial enterprise," one written proposal obtained by the AP said. Behind the scenes, ZunZuneo's computers were also storing and analyzing subscribers' messages and other demographic information, including gender, age, "receptiveness" and "political tendencies." USAID believed the demographics on dissent could help it target its other Cuba programs and "maximize our possibilities to extend our reach.".

"It was such a marvelous thing," said Ernesto Guerra, a Cuban user who never suspected his beloved network had ties to Washington.

"How was I supposed to realize that?" Guerra asked in an interview in Havana. "It's not like there was a sign saying, 'Welcome to ZunZuneo, brought to you by USAID.'"

Executives set up a corporation in Spain and an operating company in the Cayman Islands - a well-known British offshore tax haven - to pay the company's bills so the "money trail will not trace back to America," a strategy memo said. That would have been a catastrophic blow, they concluded, because it would undermine the service's credibility with subscribers and get shut down by the Cuban government.

Similarly, subscribers' messages were funneled through two other countries - but never through American-based computer servers.

Denver-based Mobile Accord considered at least a dozen candidates to head the European front company. One candidate, Francoise de Valera, told the AP she was told nothing about Cuba or U.S. involvement.

James Eberhard, Mobile Accord's CEO and a key player in the project's development, declined to comment. Creative Associates referred questions to USAID.

For more than two years, ZunZuneo grew and reached at least 40,000 subscribers. But documents reveal the team found evidence Cuban officials tried to trace the text messages and break into the ZunZuneo system. USAID told the AP that ZunZuneo stopped in September 2012 when a government grant ended.

ZunZuneo vanished abruptly in 2012, and the Communist Party remains in power - with no Cuban Spring on the horizon.

"The moment when ZunZuneo disappeared, (it) was like a vacuum," said Guerra, the ZunZuneo user. "In the end, we never learned what happened. We never learned where it came from."