PricewaterhouseCoopers said Wednesday it has not found evidence of unauthorized data access despite a group's claim that Republican presidential candidate Mitt Romney's tax returns were stolen in a late-night office theft. The financial consultancy said it is working with the U.S. Secret Service. Officials from the law enforcement agency did not have an immediate comment late Wednesday."At this time there is no evidence that our systems have been compromised or that there was any unauthorized access to the data in question," according to an email statement from Maggie O'Donovan-Bolton, PWC's tax public relations director, in New York.An unnamed group offered the documents on Sunday on Pastebin, writing that it obtained access to network file servers at PWC's offices in Franklin, Tennessee. The group is threatening to release the key to the documents, which are encrypted, if it does not receive US$1 million by Sept. 28.Romney had refused calls to release his tax returns before 2010, facing criticism that he uses complicated yet legal maneuvers to pay a much lower tax rate than most U.S. citizens.The group contends it gained access on Aug. 25 to PWC's facility through someone working on the third floor. Romney's tax returns prior to 2010, stored on the second floor in suite 260, were copied during the night, the group said. The encrypted documents were delivered on flash drives to Democrat and Republican offices in Williamson County, PWC and will be sent to major news organizations.Ken Whitehouse, senior reporter with The City News in Nashville, visited the Republican offices in downtown Franklin on Wednesday, where he was shown a manilla envelope containing the flash drive and a letter. The envelope, with crude writing and misspelled words, was hand-delivered and had no stamps, he said.Whitehouse, who said he received a tip about the alleged hacking and is credited with breaking the story, wasn't allowed to take photos or examine the flash drive. When officials emptied the envelope on a table, "they didn't want to touch it," he said in an interview Wednesday night. "When they were done, they kind of opened the envelope and scooped [the contents] back in."The group wants the money paid using the BitCoin digital currency, which is hard to trace, in order to prevent the decryption key from being released."It does not matter if small amounts or one large amount is transferred, as long as the final value of the BitCoins is equal to $1,000,000 USD at the time when it is finished," the group wrote. "The keys to unlock the data will be purged and what ever is inside the documents will remain a secret forever."Efforts to reach the Romney campaign were not immediately successful.