(CNN) -- An anonymous group says it stole copies of GOP presidential nominee Mitt Romney's tax records and will release them unless the company it stole them from pays $1 million. The Secret Service said it is investigating, and the company said there is no immediate sign that any such theft took place. "Using your office" in Franklin, Tennessee, the group tells PricewaterhouseCoopers in an online posting, "we were able to gain access to your network file servers and copy over the tax documents for one Willard M Romney and Ann D Romney." It threatens to send encrypted copies to "all major news outlets" and warns, "If the parties interested do not want the encrypted key released to the public to unlock these documents on September 28 of this year then payment will be necessary."
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NEW: A Bitcoin developer says such a heist seems unlikely
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An unnamed group demands $1 million in Bitcoins, an online currency
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Mitt Romney has not responded publicly,
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The Secret Service is investigating
The company has more than 80 offices around the country and there's nothing unique about the one in @placeholder, he said.