Jenna Fischer is finally revealing what she was typing in all those scenes on “The Office.”

While Fischer’s character, receptionist Pam Beesly, appeared to be working hard in the background of various episodes, the actor shared that she was actually chatting with her co-stars — on AOL Instant Messenger.

“John Krasinski went around to our computers and set up instant message,” Fischer said on the “Office Ladies” podcast, which she co-hosts with fellow “Office” star Angela Kinsey. “When we got the internet, he did this so that we could joke around in the background of scenes ... and I got to work one day, and he was like, ‘Check it out.’”

The NBC sitcom famously chronicled the hilarious mundanities of working at the fictional paper company Dunder Mifflin. While it’s unclear whether Krasinski — who played Pam’s love interest Jim Halpert — chose everyone else’s screen name, he certainly picked Fischer’s.

The actor recalled him showing her the “little instant message screen” only to find out she had been dubbed “receptionitis15.” Kinsey, who played conservative accountant Angela Martin in the show, added that the cast was pretty particular about their names.

“I remember that he talked us through, the rest of us, how to do it,” Kinsey said on the podcast, adding that she picked “MSaccountant” as her screen name. “We were so tickled that we could now IM each other during scenes. … We really kept on theme for our characters.”

Eagle-eyed fans of the show have long noted that Rainn Wilson chose “MonkeyTrainer” for his screen name, that is, at least for his private chats with Martin — who went by “Monkey.” Some of the actors also started branching out, however, and went on to message actual fans online.

“I would IM with fans during scenes,” Fischer shared on the podcast.

“Somehow I would get the IMs of fans through MySpace,” she added, “and I would write things, and I would say, ‘When you watch the episode “Healthcare,” there’s going to be a scene where Dwight is talking about hot dog fingers, and I’m IMing you during this scene.’”

Kinsey ultimately remained true to her character, meanwhile, and didn’t dare socialize with strangers — even from a distance.

“I kinda remember now you guys doing that,” she said on the podcast. “And we’d be like, ‘What? You’re talking to people right now?!’”