His biographer says he views the internet as a place for "porn, thievery and hackers", so why has octogenarian media mogul Rupert Murdoch suddenly joined Twitter?

The microblogging site has been around for almost five years, so why did he sign up now, and on New Year's Eve?

So far, Mr Murdoch, who has amassed almost 100,000 followers, won't say.

The move has sparked considerable speculation – could he be toying with investing in the company, as his mate Alan Sugar suggested? Was he just bored? Or was it, as one social media expert described, "the ultimate exercise in reputation management"?

Is he looking to invest?

Saudi Prince Alwaleed bin Talal's Kingdom Holding last month invested $US300 million in Twitter, in a deal big enough to value the company at more than $US8 billion.

Prince Alwaleed is closely linked to Mr Murdoch. With a 7 per cent stake in News Corp, he is the largest shareholder outside the Murdoch family and recently backed the reappointment of Rupert and his sons James and Lachlan to the News Corp board, despite widespread shareholder revolt following the phone hacking scandal in Britain.

Mr Sugar, a British entrepreneur and billionaire, tweeted: "I wonder is my old pal @rupertmurdoch is eying up Twitter to buy or invest in it. He missed out on Facebook and MySpace ... not a great deal."

But Andrew Anagnostellis, head of telecom, media and technology research at Deutsche Bank in Sydney, said he did not expect News Corp to move to acquire direct stakes in established online platforms.

"They appear to be focused on leveraging their content across many platforms," he said.

Perhaps Mr Murdoch's failed $580 million investment in MySpace, which he sold last year for $US35 million, had an effect on his confidence in new-age internet start-ups.

Perhaps he was bored on holiday?

Another possible explanation is that he was bored on his 184-foot yacht. The New York Times reported he joined Twitter while on the yacht during a Caribbean vacation with his family.

The paper said he joined while he was playing with his iPad and did not consult the company's communications staff before starting to tweet.

The day he joined the site, Mr Murdoch attended Russian oligarch Roman Abramovich's New Year's Eve party in St Barts. Some speculated he may have been trying to impress the tweet-savvy guests at the party such as Russell Simmons, Martha Stewart and Twitter chairman Jack Dorsey.

... or is it just a cynical PR campaign?

Some online reputation management experts believe he may be trying to burnish his image following the disastrous phone hacking scandal, which disgusted people around the world and dented his image.

"Rupert Murdoch's entry into the Twittersphere may well be the ultimate exercise in reputation management," independent social media consultant Thomas Tudehope said.

"In the wake of the News of the World hacking scandal that has done significant damage to his own brand, and that of News Ltd, Murdoch may well hope that by using Twitter he can engage and re-engage with an audience on a personal and direct level."

Mr Tudehope said Twitter gave Mr Murdoch a one-to-one, unedited, unscripted and unfiltered dialogue. But perhaps this is a double-edged sword, as Mr Tudehope points out that Mr Murdoch's tweets have been "littered with errors".

Tiphereth Gloria, social media strategist with George Patterson Y&R, said the explanation might be as simple as the new iOS update Mr Murdoch would have received on his iPad.

"Because of Apple integrating Twitter into the operating system of the iPad, it's made a lot more people aware of Twitter and curious enough to sign up and start using it," she said.

"All his tweets so far, have been from his iPad."

Gloria noted that, apart from the spelling mistakes, Mr Murdoch has struggled to figure out how to reply to other tweeters or mention them in his tweets, citing a recent attempt to tweet to controversial News Ltd columnist Andrew Bolt.

Tweeting up a storm

Mr Murdoch began his tweet stream with some musings on his vacation and promo tweets about upcoming Fox films. He caused controversy when he said "maybe Brits have too many holidays for broke country".

He has also voiced his support for Republican presidential candidate Rick Santorum, New York mayor Mike Bloomberg and Scotland's first minister, Alex Salmond, while he agreed with US President Barack Obama's "courageous" stance on terrorist detention.

He also tweeted that he saw education policy as the biggest crisis in the US, while Walter Isaacson's biography of Steve Jobs was "interesting but unfair".

Mr Murdoch's tweets have put some noses out of joint – he himself tweeted he was "getting killed for fooling around here" by friends scared of what he might say – but, as some have said, at least he's expressing some real opinions.

This reporter is on Twitter: @ashermoses