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marketing campaigns, target influential users or even try to predict certain events, reports the BBC.
Previously, only 30 days of tweets were made available to companies to search through. Datasift, the British company offering the archive, said its customers would be able to use access "historical" tweets from today.
"No-one's ever done this before," Tim Barker, Datasift's marketing manager, told the BBC.
"It's a brand new service that we're bringing online - it's a massive technology challenge because of the amount of data that is pumped out every single day."
The company analyses approximately 250 million tweets every day, which are searched for content, including activity around a certain term or topic and whether the "chatter" is positive or negative.
The move by Twitter has caused concern among privacy campaigners.
"People have historically used Twitter to communicate with friends and networks in the belief that their tweets will quickly disappear into the ether," argued Gus Hosein, executive director of Privacy International.
"The fact that two years' worth of tweets can now be mined for information and the resulting 'insights' sold to businesses is a radical shift in the wrong direction.
"Twitter has turned a social network that was meant to promote real-time global conversation into a vast market-research enterprise with unwilling, unpaid participants."
Mr Barker pointed out that people use Twitter due to its public nature.
"The thing with Twitter that it was always created to be a public social network - which isn't the case with Facebook which is more of a blended model. Twitter has been public from day one.
"I don't see that this creates any new dilemmas because this information is being pushed out socially right now.
"What Datasift will do is help companies get a longer view of this and a better insight."
However, the real marketing power of Twitter lies not with "historical" material, but with real-time search according to Ben Page, chief executive of research firm Ipsos-Mori
"I think the archive is in some ways less interesting. It's great that it's there, and people will look at it, but I don't think it's game-changing," he told the BBC.
But Mr Page added that any tool that claims to offer an insight into the often complex world of consumer behaviour will be welcomed by businesses.
"It will help the [businesses] who are trying to deal with consumers via social media target their activities a bit more.
"Whether they admit it or not, companies will use that."
What do you think - is it a natural step or should we be concerned?Leave a comment below...