Jeff Passan explains the difference between the sign-stealing accusations against the Astros and the Red Sox. (2:15)

The Boston Red Sox used their video replay room to steal signs from opposing pitchers and catchers during their 2018 World Series championship season, according to a report published Tuesday by The Athletic.

Citing three anonymous people who were with the Red Sox in 2018, The Athletic reported that Boston players would visit the replay room to decipher their opponents' sign sequence and then relay the information to the dugout.

Someone from the Red Sox dugout would then communicate with a baserunner, who would use body movements to relay pitch information to the batter.

"We were recently made aware of allegations suggesting the inappropriate use of our video replay room," the Red Sox said in a statement to The Athletic. "We take these allegations seriously and will fully cooperate with MLB as they investigate the matter."

The use of the video room for sign stealing, which one Red Sox source described to The Athletic as "cheating," was a practice only during the 2018 regular season, according to the report.

Multiple Red Sox sources told The Athletic that the system was impossible to use during the postseason because Major League Baseball had in-person monitors stationed in all video replay rooms during the playoffs.

"It's cheating," a source who was with the Red Sox in 2018 told The Athletic. "Because if you're using a camera to zoom in on the crotch of the catcher, to break down the sign system, and then take that information and give it out to the runner, then he doesn't have to steal it."

Major League Baseball told The Athletic that it will investigate the allegations against the Red Sox.

"The Commissioner made clear in a September 15, 2017, memorandum to clubs how seriously he would take any future violation of the regulations regarding use of electronic equipment or the inappropriate use of the video replay room," MLB said in its statement to The Athletic. "Given these allegations, MLB will commence an investigation into this matter."

As part of its crackdown on electronic sign stealing late in 2017 and before the 2018 season, MLB stated in a memo to all 30 teams that all "electronic equipment, including game feeds in the Club replay room and/or video room, may never be used during a game for the purpose of stealing the opposing team's signs."

Red Sox manager Alex Cora, who guided Boston to the World Series title in his debut 2018 season, could also be facing discipline as part of MLB's investigation of the 2017 Houston Astros for alleged sign stealing.

Cora was the Astros' bench coach in 2017. The Red Sox have declined to comment to The Athletic on Tuesday's report.