Background to 'Assessing Russian Activities and Intentions in Recent US Elections': The Analytic Process and Cyber Incident Attribution [open pdf - 2MB]
"'Assessing Russian Activities and Intentions in Recent US Elections' is a declassified version of a highly classified assessment that has been provided to the President and to recipients approved by the President.  The Intelligence Community rarely can publicly reveal the full extent of its knowledge or the precise bases for its assessments, as the release of such information would reveal sensitive sources or methods and imperil the ability to collect critical foreign intelligence in the future.  Thus, while the conclusions in the report are all reflected in the classified assessment, the declassified report does not and cannot include the full supporting information, including specific intelligence and sources and methods. [...] This report includes an analytic assessment drafted and coordinated among The Central Intelligence Agency (CIA), The Federal Bureau of Investigation (FBI), and The National Security Agency (NSA), which draws on intelligence information collected and disseminated by those three agencies. It covers the motivation and scope of Moscow's intentions regarding US elections and Moscow's use of cyber tools and media campaigns to influence US public opinion. The assessment focuses on activities aimed at the 2016 US presidential election and draws on our understanding of previous Russian influence operations. When we use the term 'we' it refers to an assessment by all three agencies."
Office of the Director of National Intelligence: http://www.dni.gov/