In the second part of the Comey testimony it was revealed Peter Strzok sent an email to Jim Rybicki admitting that foreign actors had obtained access to Hillary's emails and at least one of these emails contained secret information.
Questioner is Robert Parmiter with the Judiciary Committee majority staff. Answerer is Comey.
Pg. 168
https://oversight.house.gov/wp-content/uploads/2018/12/Comey-Interview-Part-Two.pdf