(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."
The group demands $1 million. It also says that people who want the documents released can send money as well, and whichever side sends $1 million first will win.
PricewaterhouseCoopers, which offers tax services as well as auditing and more, tweeted that it is "working with the Secret Service. At this time, there is no evidence of unauthorized access to our data."
The anonymous postings say that copies of the stolen material have been sent to the company, as well as to the county Democratic and Republican offices, and that a scanned image of Romney's signature from the forms was included.
Party officials in Williamson County, Tennessee, could not be reached immediately Thursday morning.
Romney released no public statement on the alleged hack.
While the postings, on the website pastebin.com, refer to "a team" involved in the alleged break-in, one ends with a line stating that certain "considerations did not deter me from the path of duty" and a reference to "the will of my Heavenly Father."
The postings go into detail about how the alleged heist was carried out.
The group says it obtained "all available 1040 tax forms for Romney," including some from before 2010, but it does not say which years.
Romney has released his 2010 and 2011 tax returns, and has said he will not release others. The issue has been a source of controversy on the campaign trail.
