CHCH and its parent company Channel Zero have investigated, and say the issue wasn't on their end, and is a carrier problem with Rogers SD service.
Fanshawe College student Gabe Burchert saw the pornography in question around 2:30 p.m. at the school's newsroom.
"I looked up, and there it is," he said from the school in London, Ont. The television was tuned to CHCH, he said. None of the other televisions in the newsroom that were set to other stations changed, he added.
The sex scene lasted for about five seconds before it switched back, he said.
"I have to admit, it was pretty funny," Burchert said.
CHCH News Director Mike Katrycz told CBC News that the problem is on a carrier's end. CH has investigated and checked its log tapes and found no adult material, he said.
"It had to be shown from some other service provider. It wasn't us," he said.
Rhonda Messieh, marketing manager for Channel Zero told CBC News that an investigation is ongoing. "Our VP of operations is all over it," she said. "It's nothing that actually occurred on our end."
She said as she understands it, the issue stemmed from a "decoder reset" at Rogers. Rogers could not immediately be reached for comment.
This is not the first time CHCH viewers have unexpectedly seen hardcore pornography.
The Hamilton-based broadcaster issued an apology back in 2012 after its morning News Now show was briefly switched for a graphic sex scene.
The station, which is owned by Toronto-based media group Channel Zero, blamed the mixup on a switching error at one of the cable companies that carries its signal.
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