The lawsuit claims that when users share a link to another website via a private message, Facebook scans it to profile the sender's web activity.

It alleges that Facebook systematically intercepts messages to mine user data and profits by sharing it with data aggregators, advertisers and marketers.

Facebook said the allegations were "without merit".

"We will defend ourselves vigorously," the world's biggest social networking site added.

The lawsuit is claiming the greater of either $100 (£61) a day for each day of alleged violations or $10,000, for each user.

The lawsuit, filed earlier this week, cites independent research that, it claims, found Facebook reviews the contents of its users' private messages "for purposes unrelated to the facilitation of message transmission".

"Representing to users that the content of Facebook messages is "private" creates an especially profitable opportunity for Facebook," it says.

It says this is "because users who believe they are communicating on a service free from surveillance are likely to reveal facts about themselves that they would not reveal had they known the content was being monitored.

"Thus, Facebook has positioned itself to acquire pieces of the users' profiles that are likely unavailable to other data aggregators."

However, others have come forward to defend Facebook.

Writing on his blog, security expert Graham Cluley said that if the site was not examining links shared privately, Facebook would be failing a "duty of care" to its users.

"If you didn't properly scan and check links there's a very real risk that spam, scams, phishing attacks, and malicious URLs designed to infect recipients' computers with malware could run rife," he argued.

Facebook has come under attack over its privacy policies in the past.

In September last year, it faced criticism over a proposed change to its privacy policy which would have allowed ads to be created using the names and profile pictures of Facebook users.

The firm had claimed that its proposal merely clarified the language of its privacy policy, rather than making any material changes to it.

Facebook undertook to change the wording in the wake of a legal action launched in 2011 which saw it pay $20m to compensate users who claimed it had used their data without explicit permission.

GM shares fell 2.4% after it reported a 6.3% fall in sales compared with December 2012.

Ford and Chrysler both reported rising sales, but not the increases that industry analysts were expecting.

Chrysler sold 161,000 cars and trucks in December, up 5.7% on the same period in 2012 and Ford reported a 1.8% rise in December sales.

Analysts said that poor weather in parts of the US kept customers away from dealerships in December.

"At the very beginning of the month the pace of buying was slow because there were so many storms around the country," said Edmunds.com senior analyst Michelle Krebs.

"Now what we're seeing is some of the automakers are stretching their December deals into January."

Kurt McNeil, vice president, of US sales for GM, said: "December started a little slow but sales were stronger later in the month, especially in the week between Christmas and New Year."

Meanwhile Ford said that a four-day weekend for Thanksgiving late in November may have brought forward sales that would have fallen in December.

For Chrysler the Jeep brand continued to be a strong performer with a 34% rise in sales last month.

With a 9% rise in annual sales, 2013 was the strongest year for Chrysler since 2007.

"Our Jeep and Ram truck brands had a strong finish led by the all new 2014 Jeep Cherokee and the Ram pickup truck," said Reid Bigland, head of US sales.

Overall, sales in 2013 were strong for the big three Detroit car manufacturers, who were helped along by strong sales of their truck offerings.

Truck sales tend to increase in relation to home sales, which were strong for much of the year as the US economic recovery spurred long-delayed housing activity.

"Trucks on the road are even older than cars on the road," said Ms Krebs.

She added: "There are lots of new products: Chrysler came out with a new Ram pick-up truck, GM introduced its new trucks this fall and Toyota had a new Tundra model" which further enticed consumers.

However, Toyota, the third biggest player in the US market, didn't do as well as the US manufacturers.

It saw sales in December decline by 1.7% from a year ago to 190,843.

Analysts had been expecting Toyota to report rising sales.

But 2013 is expected to be the best year for US auto market since 2007, with total annual sales of about 15.6 million.

That would be a strong recovery from 2009 when sales fell to 10.4 million during the depths of the recession.

Spain's public works minister Ana Pastor will fly to Panama this weekend, following a meeting between diplomats on Friday.

Work began on the expansion of the shipping hub in 2009, but it has gone over-budget by $1.6bn (£1bn).

The group behind the project, led by Spain's Sacyr, has threatened to halt work unless the extra money is paid.

Sacyr's chairman Manuel Manrique will also fly to Panama to join in the negotiations.

The building group, known as the Grupo Unidos por el Canal (GUPC), is made up of Spain's Sacyr, Italy's Salini Impreglio, Belgium's Jan De Nul, and Panama's Constructora Urbana.

It is in the process of constructing a third lock which will allow bigger ships to pass through.

It gave a 21 day deadline on 30 December to the Panama Canal Authority to make the extra $1.6 billion payment. If it doesn't, GUPC says it will stop work on the expansion plans.

A spokesperson for Spain's foreign ministry said: "Panama is a country that is close and friendly towards Spain, and we share the desire and interest to find a solution as soon as possible".

Spain's ambassador to Panama, Jesus Silva, added that all stand to lose out if the contract fell through.

On Thursday, Panama's President Ricardo Martinelli threatened to demand that the building consortium fulfil its contract to expand the canal.

The president said: "I will go to Spain and Italy to demand these governments take moral responsibility."

Construction is due to be completed in June 2015, nine months behind schedule. The overall cost of the project now expected to be $5.2bn.

Building work is now focused on the creation of a third set of locks to accommodate ships that can carry 12,000 containers. The largest ships currently able to navigate the Panama Canal carry 5,000.

The Panama Canal handles 5% of the world's maritime trade.

Kanye West is not involved and has yet to comment on its inception.

It will follow in the footsteps of "Dogecoin", another virtual currency based on the popular Doge meme.

The value of Bitcoin, the most famous virtual currency, peaked at over $1000 (£613) last year but is currently worth around $850 (£520).

Various alternatives to Bitcoin have sprung up, such as Litecoin, Namecoin and PPCoin.

Virtual currencies are often linked to the purchase of illegal items, namely drugs, thanks to transactions being extremely difficult to trace.

However, more humorous currencies like Dogecoin are used for more tongue-in-cheek transactions.

One user, posting on Dogemarket, a section on popular link sharing site Reddit, offered Dogecoins in exchange for ideas to name a company.

"I thought the whole Dogecoin thing was interesting," said Jeremy Bonney, from virtual currency news site Coindesk.

"It grew into something somewhat legitimate. There are people that genuinely believe in it out there."

The makers of Coinye West have lofty ambitions for the currency which they described as a "cryptocurrency for the masses".

Speaking anonymously to music site Noisey, they said: "I can picture a future where Coinye is used to buy concert tickets, with cryptographically verified virtual tickets, and other ideas I can't give away just yet."

They said they planned to give away a number of Coinye to early users when the currency launches on 11 January.

"It will get people who are on the fence interested and help them to start using the currency, and we hope they'll share it with their friends, too."

However, one Bitcoin expert urged caution in investing in new virtual currencies that were as yet untested in public use.

"There's been a number of people who have put out 'joke' currencies in the past," said Johnathan Turrall, chief technology officer atMetalair, a cryptocurrency start-up based at the University of Sussex.

"There were some coins in the past that seemed to be a 'pump and dump' operation.

"In one case, the original developers launched on obscure websites, but when they took it mainstream, and the price spiked, they sold up and disappeared. Estimated earnings in one instance were $800,000."

Mike Hearn, a Bitcoin developer, said Coinye West was, at the very least, an expression of the "democratic" nature of the technology behind virtual currencies.

HTC said that its net profit in the three months to December were 300m Taiwan dollars ($10m; £6m), compared to 1bn Taiwan dollars in the same period last year.

Analysts had been expecting a much larger profit.

HTC has lost nearly three-quarters of its market value in the past two years.

The Taiwanese company reported its first-ever loss in the previous quarter.

And this fourth-quarter profit figure included a one-time gain from selling its stake in the Dr Dre-backed headphone brand Beats Electronics.

HTC was one of the early market leaders in smartphones running Google's Android software, but has lost market share to rivals such as Samsung in recent years.

It has launched new products, such as the HTC One, in an attempt to regain some of the lost ground, but they have yet to be a huge hit with consumers.

The company's global share of the smartphone market declined to 2.2% in the third quarter of 2013, from a peak of 10.3% two years earlier, according to data from research firm Gartner.

Zynga is perhaps the most significant video games firm to accept bitcoins to date.

The virtual currency has been gaining in popularity but its value has been highly volatile in recent weeks.

It peaked at $1,250 in November last year, but fell sharply in December after China restricted trade.

According to the South China Morning Post, the value of a single Bitcoin fell to as low as 2,560 yuan ($421, £258) in December, after China's move.

On Monday, a single Bitcoin was trading close to $1,030 on MTGox, one of the virtual currency's major exchanges.

Zynga follows Ouya, the Android-based video games console-maker, which began accepting payments for its hardware in bitcoins last month.

The Humble Bundle - an organisation selling a changing selection of indie games - also began accepting bitcoins in 2013.

Supporters of Bitcoin, which is not backed by a central bank, have been pushing for its increased usage.

Its popularity and value surged last year after a US Senate committee described virtual currencies as a "legitimate financial service".

Zynga said it had tied up with BitPay, a Bitcoin payment service, to allow users to purchase virtual goods in some of its games using the facility.

"In response to Bitcoin's rise in popularity around the world, Zynga, with help from BitPay, is testing expanded payment options for players to make in-game purchases using Bitcoin," the firm said in a post on Reddit.

Bitcoin became popular, in part, due to it being difficult to trace transactions that use it. The currency has been linked to illegal activity online.

Last month, the European Banking Authority (EBA) warned the public about the potential risks of using bitcoins.

"Currently, no specific regulatory protections exist in the European Union that would protect consumers from financial losses if a platform that exchanges or holds virtual currencies fails or goes out of business," the EBA said.

China, the world's second largest economy, has also banned its banks from handling Bitcoin transactions, saying they had no legal status and should not be used as a currency.

At the same time, there have been concerns that the rise in Bitcoin's value has been triggered by speculators looking to cash in on its popularity.

Alan Greenspan, former US Federal Reserve chairman, has called the rapid rise a "bubble".