Facebook at Work is a new smartphone app that will allow staff to interactive with each other within a company. Picture: AP

San Francisco - Facebook will let advertisers know where a promotion was first viewed and when it led to a purchase by tracking users between their electronic devices, a tool that may reignite privacy concerns.

Marketers will be able to see the number of users that clicked on an ad, whether they used a smartphone, tablet or desktop computer, and which device was used to buy a product, Menlo Park, California-based Facebook said in a blog post on Wednesday.

Facebook has been bulking up advertising services as the social network's mobile ads propel revenue and profit. While users and privacy watchdogs around the world criticise Facebook's use of personal data, the company is under pressure from advertisers to prove that their mobile promotions are effective.

As Facebook finds new ways to analyse the behaviour of its more than 1 billion users, controversy has emerged regarding its methods. A Facebook data scientist apologised in June after conducting an experiment that temporarily influenced what almost 700 000 readers saw on their news feeds without getting permission.

With the new cross-device service announced on Wednesday, Facebook is aiming to prove that mobile ads can lead to purchases, even if those purchases aren't necessarily made on a smartphone. In a study with Altimeter Group, Facebook found that among people who showed interest in a mobile ad, more than 32 percent took action on desktop computers within 28 days.

Because Facebook's users must log in to use the service, the company can link their identities with their behaviour as they switch between devices throughout the day. That allows Facebook to give more information to marketers than they could glean from other online tracking methods, such as cookies that log activity within a Web browser.

“With the new cross-device report, advertisers are now able to see where someone saw an ad, the device they used, and which device was used when they converted,” Facebook said today in the blog post.

Facebook has extended its advertising empire outside its main application. Earlier this year, the company opened up its network of advertisers to software developers who were given the option to run Facebook ads on their applications. Facebook recently agreed to acquire LiveRail, which will help it serve video advertisements outside of Facebook itself. - Bloomberg/Washington Post