According to a June 17, 2016 Bloomberg News article, during this time period, the same allegedly Russian hackers who breach the computers of the DNC [Democratic National Committee] and Clinton’s presidential campaign “[burrow] much further into the US political system, sweeping in law firms, lobbyists, consultants, foundations, and the policy groups known as think tanks, according to a person familiar with investigations of the attacks.” Almost 4,000 Google accounts are targeted by “spear phishing,” which involves tricking targets to give log-in information so their data can be accessed. The Center for American Progress, a think tank with ties to Clinton and the Obama administration, is one known target.
Bloomberg News will further report that, “Based on data now being analyzed, various security researchers believe the campaign stems from hackers linked to Russian intelligence services and has been broadly successful, extracting reams of reports, policy papers, correspondence and other information.”
The Russian government denies any involvement, but cybersecurity experts who have investigated the attacks believe the hackers are working for Russia. It is believed that either or both of two major Russian hacking groups, Fancy Bear (or APT 28) and Cozy Bear (or APT 29) are behind the attacks. (Bloomberg News, 6/17/2016)