The DNC network was hacked by Russian hackers belonging to nation-state groups that have had access to the groups communications and databases. CrowdStrike’s incident response time discovered not one, but two hacking groups that it considers some of the best adversaries groups the company encounters daily. In February of this year, Director of National Intelligence James Clapper told congress that intelligence officials were already seeing targeting of the 2016 presidential campaigns. In April 2015, experts at Kaspersky Lab uncovered the CozyDuke that targeted several high-profile organizations in the second half of 2014.”]
Source: https://securityaffairs.co/wordpress/48428/intelligence/russian-hackers-spy-us-politics.html