The blog said the hacker sent a USB drive and letter to the Republican and Democratic party offices in Williamson County, Tenn., as proof the claim was not a hoax. The letter says the tax returns were stolen from PricewaterhouseCoopers in Franklin, Tenn.
The letter threatens to turn the returns over to the news media. The hacker wants the money in Bitcoins, a form of electronic cash.
Williamson County Republican party Executive Director Jean Barwick told VentureBeat the U.S. Secret Service has taken the letter and the USB drive from the GOP party office for an investigation.
"We don't know what this will turn into if anything," Barwick told the blog. "[The Secret Service] didn't say what they would do with it."
VentureBeat said PricewaterhouseCoopers PR managing director Chris Atkins said in an e-mail: "We are working closely with the United States Secret Service, and 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."