New York, Dec 29 (IANS): Facebook already knows a lot about your online activities and you are pretty much aware of it. But a new media investigation has revealed that the social networking giant buys data on your offline activities without your knowledge.

The information that Facebook collects can include things like how much money you make, the stores you shop in, and even the number of credit cards you own, according to the investigation by ProPublica.

At the heart of the issue is that the tech giant gives users little indication that it buys far more sensitive data about them than what the social media platform declares it knows. 

Facebook uses algorithms to categorise its users in tens of thousands of micro-targetable groups for advertisers.

"Facebook's site says it gets information about its users 'from a few different sources'," ProPublica said in its report on Tuesday.

"What the page doesn't say is that those sources include detailed dossiers obtained from commercial data brokers about users' offline lives. Nor does Facebook show users any of the often remarkably detailed information it gets from those brokers," it added.

"They are not being honest," Jeffrey Chester, Executive Director of the Center for Digital Democracy, was quoted as saying.

"Facebook is bundling a dozen different data companies to target an individual customer, and an individual should have access to that bundle as well," Chester noted.