The personal details of more than a fifth of Facebook’s estimated 500 million users have been "leaked" to the internet by campaigners highlighting its "terrifying" privacy fears.
The list, which has been published in a downloadable file, contains the URL of every searchable Facebook user’s profiles, their names and unique ID.
Campaigners warned the list, published on “Pirate Bay”, the world's biggest filesharing website, affected more than 100 million users on the social networking site.
On Wednesday, the list was rapidly spreading across the internet being distributed and downloaded by more than 1,000 users, the BBC reported. One user described the list as "awesome and a little terrifying".
But its publication provoked concern from privacy experts who said it proved Facebook’s “confusing” privacy settings were still apparent.
But the company defended its privacy settings and denied any “private data” had been made available or comprised, saying the information was already available.
Last week Facebook reached 500 million members – the equivalent of connecting with eight per cent of the world’s population. If it were a country, its 500 million members would make it the third-largest country in the world.
The list was “leaked” to the site by Ron Bowles, an online security consultant, who reportedly used a simple piece of code to collect the data from the site.
He told the broadcaster that he published the data to highlight privacy issues.
Simon Davies, of Privacy International, a campaign group, said:"Facebook should have anticipated this attack and put measures in place to prevent it," he said.
"It is inconceivable that a firm with hundreds of engineers couldn't have imagined a trawl of this magnitude and there's an argument to be heard that Facebook have acted with negligence.”
He added: "This highlights the argument for a higher level of privacy and proves the case for default nondisclosure.
"There are going to be a lot of angry and concerned people right now who be wondering who has their data and what they should do."
In a statement to the BBC, Facebook said the list’s information was already freely available online.
"People who use Facebook own their information and have the right to share only what they want, with whom they want, and when they want," a spokesman said.
"In this case, information that people have agreed to make public was collected by a single researcher and already exists in Google, Bing, other search engines, as well as on Facebook.
"No private data is available or has been compromised.”
He added: “It is similar to the white pages of the phone book, this is the information available to enable people to find each other, which is the reason people join Facebook.
"If someone does not want to be found, we also offer a number of controls to enable people not to appear in search on Facebook, in search engines, or share any information with applications."
Mark Zuckerberg, Facebook’s founder and chief executive, has said he believes the company has got its privacy settings right “on the whole”.
The site recently faced a storm of international protest over its over-complicated privacy settings, which users said led them unwittingly to make personal information public.
It forced the social networking site to announced last month that it would “drastically simplify” the controls that let users set how much of their personal information is visible to other users.
Telegraph Media Group Limited