The Senate Committee on Intelligence released a highly redacted report saying that Russia hackers targeted the voting systems of all 50 states during the 2016 elections, and while there is no evidence of tampering, it’s clear that they could have altered votes in some systems.

The original report from the Senate can be found on the official website at:
https://www.intelligence.senate.gov/sites/default/files/documents/Report_Volume1.pdf

Learn more from these news articles:

New York Times
https://www.nytimes.com/2019/07/25/us/politics/russian-hacking-elections.html 

The Verge
https://www.theverge.com/2019/7/25/8930985/russia-targeted-election-systems-in-all-50-states-senate-concludes

Washington Post
https://www.washingtonpost.com/opinions/2019/07/30/high-level-senate-report-confirms-it-our-elections-still-arent-safe/?utm_term=.ec22bd2e139b

Vanity Fair
https://www.vanityfair.com/news/2019/07/senate-report-russia-2016-election-50-states