TORONTO - When their story about a condo developer who forgot to put bathrooms in a Toronto-area highrise went viral last week, writers at the CBC's satirical show "This Is That" were faced with an unexpected conundrum: many of the people who heard, read or shared the story online thought it was true.

It wasn't the first time that readers and listeners had taken the show at face value — the radio program regularly plays voicemail messages from people who mistake it for real news — but enough people flagged it to the CBC this time that the public broadcaster took a drastic step to clear up any possible misunderstanding.

It changed the show's headlines to include one word, in capital letters: "SATIRE."

"What we immediately realized is we have to take action right now because the last thing we want is to fool people and damage our news brand," said Jeff Ulster, director of digital talk content for CBC Radio.

"So we put 'satire' in the headline, which I think is very heavy-handed, but we did it because we thought in the list of priorities that's further down than making sure no one thinks we're actually trying to deliver a news story to them."

Part of the problem is that people were only reading the headline, which appeared on Facebook, Twitter and other sites under the CBC banner without any indication it came from the broadcaster's comedy site, Ulster said. The network is working to resolve how headlines are displayed on social media, he said.

But CBC is hardly the only one to have duped unsuspecting readers with its humour. In recent years, stories from the renowned satire site The Onion have been republished in foreign newspapers and prompted at least one police investigation. Its stories are so often posted as real on Facebook — typically with outraged comments — that at least one site is dedicated to highlighting such incidents.

Some experts say the proliferation of news sources and satire, as well as the ease and speed of social media — combined with readers' short attention spans — make it easy for a fraction of readers to fall for fake news. And no one is fully immune, they say.

A decade or so ago, there were few satire news outlets, with The Onion largely dominating the online market. Since then, it has been joined by multiple competitors including the Canadian joke news site The Beaverton, the satirical music news site The Hard Times, and a spoof of women's magazines called Reductress.

Some have suggested the prevalence of potentially believable spoofs could undermine political discourse or faith in the media, though in most cases the confusion is temporary and leads only to short-lived embarrassment.

The shift toward Internet-friendly buzzy stories with attention-grabbing headlines in real news may also help blur the lines, said Gavin Adamson, a journalism professor at Ryerson University.

"There's something in there that fulfills our desire for hearing something outrageous," he said. "This doesn't just happen with fake news — it happens with real news too. You see often the most read news is something just bizarre and actually unbelievable but sometimes the unbelievable does happen."

"Sometimes fake news takes advantage of that," he said.

Social media also exposes people to stories from sites they might otherwise never come across and they may be caught unawares, he said.

"Your skepticism isn't really at its peak sometimes when you're just floating through Facebook or Twitter, you're really just trying to entertain yourself," Adamson said. 'And I think social media can really lower your guard in many instances."

Compounding that is the fact that many people don't read stories all the way through, and may miss important cues, he said.

A person's state of mind, including whether they are distracted, can contribute to their susceptibility, said Stephen Greenspan, author of "Annals of Gullibility: Why We Get Duped and How To Avoid It." People are also more likely to believe something that reflects their existing convictions, he said.

Circumstances — whether someone is under pressure or rushed — and a person's knowledge of the topic, as well as their personality, can also play a role, he said.

"Everybody can be fooled," he said, adding the key is to not make the same mistake over and over.

Over time, most satire sites are recognized as such by the initially unsuspecting. For the CBC, however, much of the confusion stems from its main function as a source of legitimate news.

On its own site, the broadcaster can control the context in which its stories are read by posting them on its comedy portal, Ulster said. But it has no power over how those stories are repackaged on aggregator sites, which help propagate these stories, he said.

In the meantime, the "This Is That" site has begun labelling its stories as satire at the top of the text as well as the bottom, since some weren't reading to the end, Ulster said.

"Even though we know there's a percentage of people, no matter what you do, will be duped, it's not the intention to make people feel stupid," he said. "We don't want people to feel stupid and I think when you share something and then you find out it's fake, you probably feel stupid. So that is not what we want."

News from © The Canadian Press, 2016