Media hoaxes are nothing new.

The Hitler Diaries fooled both the Sunday Times and the German magazine Stern. A fake website about the Bhopal disaster hoodwinked the BBC. But social networking sites mean hoaxes can now travel faster, unchecked, than ever before.

Could this week's reports about the French president Nicolas Sarkozy and Carla Bruni stem from another hoax

That is the latest claim, after rumours about the couple swept France via Twitter and found their way into some British media.

A front page headline in Wednesday's Daily Telegraph proclaimed, "Sarkozy affair rumours sweep France". Over prominent photographs of Carla Bruni and another woman, the paper asked "Has Carla met her match"

The Daily Mail asked: "Are Sarko and Carla cheating on each other" and reported, "they are, if the rumour mill is to be believed, both having affairs."

The Independent's website carried a Press Association report which acknowledged the rumours, but pointed out that the mainstream French media had not reported them.

"Paris gossips were trying to sort out fact from fiction today as the blogosphere raised tantalising questions about the glamorous pop 'n' politics marriage of President Nicolas Sarkozy and Carla Bruni," it read.

"While the 'traditional' French media remained silent, bloggers and Twitterers spread word of alleged infidelity in high places - on both sides."

'Cruel hoax'

The reports in Britain prompted Sky News to bring forward a pre-recorded interview with Carla Bruni, in which she was asked whether she believed her husband had had affairs in the past.

That in turn led to reports that she had denied the current speculation, with online headlines such as: "Carla Bruni denies affair rumours sparked by Twitter and internet gossip".

Should newspapers, broadcasters or news agencies such as the Press Association report such unconfirmed rumours It's a growing problem for all mainstream media, as news stories spread via Twitter, blogs and other social media networks. Is the fact that a rumour is spreading rapidly a sufficient justification to report it

If so, the Sarkozy claims should act as a warning. For the next day's Independent carried a new line from its Paris correspondent, John Lichfield, under the headline "End of the affair Or a cruel hoax"

He wrote: "According to one French magazine, L'Express, the rumour began as a hoax by a French trainee journalist.

"He wanted to see how easy it was to get an unverified assertion from the chat website Twitter on to random blogs and into the mainstream media. If so, he succeeded beyond his wildest dreams."

But Lichfield went on: "The L'Express report of a hoax cannot be verified either. No one has yet come forward to claim the credit for starting the rumour rolling."

That story in turn was rapidly "retweeted" across the blogosphere, leaving no one any clearer at this stage whether the rumours were a hoax or had any justification at all.

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