The Bradley Files were originally made public in October 2016, by unknown persons claiming to be part of the hacking collective known as “Anonymous.” Two twitter accounts @AnonymousGlobo and @AnPoland took credit for the document release.
Some private security firms, such as ThreatConnect, have noted that the @AnPoland account appears linked to @FancyBearHT. ThreatConnect pointed to an August 2016 incident when @AnPoland announced it would soon publish a database from the World Anti-Doping Agency (WADA). But the confidential athlete files, including those of U.S. Olympians Simone Biles and Serena Williams, were released to the public by Fancy Bear Hack Team @FancyBearHT. In June 2016, Crowdstrike, the cyber firm called in to handle the Democratic National Committee (DNC) breach, named @FancyBearHT as a “Russian based threat actor” and one of two hackers of the DNC.
The Bradley hacker(s) obtained and made public more than 30GB of data about the Bradley Foundation’s activities. They also inserted and publicized a forged letter making it appear that the Bradley Foundation gave $150 million to Hillary Clinton’s campaign. The Bradley Foundation acknowledged in a statement that it was “aware of an unauthorized cyber intrusion into our network that also resulted in the production of a fraudulent letter” and that the hack was under investigation by the FBI.
Why sophisticated hackers would target the right-wing Bradley Foundation is not known. However, Bradley does fund a wide array of foreign policy research and advocacy, including research on the Russia-Ukraine conflict. In addition in July 2016, Michael Grebe gave up his delegate slot to the Republican National Conventions stating he wanted no role in the nomination of Donald Trump.
For more analysis of the ties to Russia, see this article from the Milwaukee Journal Sentinel.