Sanders said he learned about the alleged interference in his campaign approximately one month ago.

Thursday's announcement was the first time the U.S. government connected the GRU to the hacking group known as Sandworm.

Winner was sentenced in 2018 after she allegedly mailed classified information from the NSA.

Iranian bots and trolls are subtler than Russia's, according to researchers at the Atlantic Council.

Operations from Iran, Malaysia and Vietnam also were identified by the social media company's researchers.

Difficulties in understanding the full scope of the Russian cyber threat hampered the administration's response.