"At first I realized I was looking at a naked woman and it quickly became clear she was having sex," Danyal Ek, a 23-year-old student from Lund in southern Sweden, told The Local.
The incident took place during a Monday morning broadcast on 24-hour Swedish news channel TV4 News as the presenter was interviewing the station's Moscow correspondent for reaction in Russia to the Syrian president's speech at the weekend.
As the two journalists discussed Russia's support of for the Syrian regime, a pornographic film began playing on one of the television screens situated behind the anchor.
"It didn't take long before I realized it was a porn film," said Ek, referring to the movements on the screen.
"The image wasn't exactly in focus, but it wasn't hard to figure out what was going on."
The erotic film was visible behind the presenter for about 10 minutes during the news broadcast, leaving Ek surprised, but not upset.
"I had two theories. One is that someone was pissed off after getting fired and put the porno up as act of revenge. My other thought was that someone had simply screwed up," he said.
TV4 news editor Andreas Haglind confirmed that that the adult film had been shown live on TV4 News, but claimed that didn't mean that a member of staff was actively watching porn.
Rather, the screen was likely tied to a computer server elsewhere in the studio connected to other channels operated by TV4-owned C More Entertainment (formerly Canal+), some of which broadcast erotic content.
"It's not like we were directly broadcasting porn," he told the Expressen newspaper.
"Put simply, it's crap that it happened. We're going to do everything we can so that it doesn't happen again."
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Ek said TV4's unexpected erotic episode didn't affect his perception of the broadcaster.
"People make mistakes," he said.