Wang Yibo accessed the cable feed to 465,000 set-top boxes in the eastern city of Wenzhou last August, state broadcaster China Central Television said.
"Bandit Communists you've done too many evil deeds and now you're feeling guilty," read one of the messages shown, viewers said at the time.
The phrase "Friends, don't co-operate with Communist devils," was imposed over a basketball match, and the emblematic photograph of a lone individual standing in front of a column of tanks during the 1989 pro-democracy protests was also shown, they said.
Wang, a Beijing-based employee of a technology firm which serviced the cable company, was detained the same month as the incident as he returned to the capital from a family vacation in the US, and confessed after two days of questioning, CCTV said.
He was sentenced last month by a court in Wenzhou and admitted carrying out the lone attack due to disappointment he was not given more "opportunities" at work, the report Monday said.
