Update: A comment from Privacy International on the Facebook/ IBM partnership has been added to this article

Facebook's partnership with IBM to deliver personalised marketing through a massive data-sharing programme has been questioned by privacy advocates.

The deal between the two tech giants aims to take targeted advertising to an entirely new level by combining Facebook's vast collection of personal data with IBM's data analytic capabilities.

Under the terms of the deal, announced on 6 May, Facebook will share its users' data with retailers and other advertising customers of the company. This data will then be used in IBM's "big data" analysis service.

Deepak Advani, general manager of IBM Commerce, said the retailers and consumer product brands that IBM already works with have been urging the company to bring the social network into the equation because "Facebook is where consumers spend a lot of their time".

'We need more than the sales pitch'

Blake Chandlee, vice president of of partnerships for Facebook, has tried to assuage the privacy concerns surrounding users' data that the IBM-Facebook partnership inevitably raises.

Chandlee claims only Facebook is able to access identifying information about its users, such as names and email addresses, stating: "Personal data never flows back and forth."

This may not be enough to satisfy some privacy advocates, though, with Facebook frequently criticised about its data collection practices and its frequent changes to its privacy policy.

"This programme raises more questions than we have answers," Jim Killock, executive director of Open Rights Group, told IBTimes UK.

"We would like to know the legal basis for this data sharing. It is unclear how Facebook and IBM's customers believe they have consent and would pass data protection standards.

"Given the nature of what they are doing, and the amount of personal information they are handling, it is extremely important they explain precisely their intentions and legal justifications. We need more than the sales pitch."

Neither IBM nor Facebook have commented on the financial terms of the deal but Advani did reveal it marked the beginning of a "very broad partnership".

Carly Nyst, legal director of Privacy International, warned of the "false promise" of anonymisation to guard against privacy invasions by advertising entities.

"We should take no consolation in Facebook reassuring us that they strip names and addresses from data before passing it on to consumer behaviour analysts," Lyst told IBTimes UK. "Particularly when it takes no more than a date of birth and a zip code to uniquely identify someone."