From ABC News:
It may have been a greater error allowing Colbert into the Fox News headquarters, located near the "Colbert Report" studios in Manhattan. There, Colbert smuggled a microwave out of the green room, a bounty which he proudly displayed at the conclusion of his show.
A spokesman for Fox News confirmed that Colbert stole the microwave, but said it was all in good fun.
HuffPo has more:
According to FNC spokeswoman Irena Briganti, Colbert told O'Reilly off-camera of his plan to take the microwave from the Green Room. "We were well aware of it and entirely amused - it was all in good fun," said Briganti in an email earlier today. "We honestly just thought the whole thing was hysterical."