Despite the fact that the social notworking site Facebook has denied being interested in what its users do on other sites, evidence has been unearthed that it has developed technology to do just that.
An Aussie blogger has found a patent, dated this month, where Facebook describes a method "for tracking information about the activities of users of a social networking system while on another domain".
Nik Cubrilovic said that tracking cookies monitor Facebook users whenever they surf websites with a Facebook 'like' button.
An Illinois man has already filed a lawsuit over the tracking on behalf of Facebook users in the US and he is seeking class action status.
Facebook claimed at the time that cookies were tracking users in error. Cubrilovic's latest post proves that Facebook has not switched the tracking off.
Facebook 's official line is that tracking cookies were only installed when users accessed Facebook.com but Cubrilovic found they were set by all sites that contained Facebook widgets.
One of the tracking cookies tracks users "even if the user had never been to the Facebook site, and even if they didn't click a 'like' or share' button", Cubrilovic wrote.
The cookie was disabled after an outcry in the The Wall Street Journal earlier this year but has quietly returned.
The patent, which has the catchy title "Communicating Information in a Social Network System about Activities from Another Domain", refers to tracking users outside of Facebook.com.
It describes maintaining a "profile" of each user as they move around the web and "logging the actions taken on the third-party website".
A Facebook spokesman said the patent was not intended to track logged out users. The idea has been patented but it has not been used, it claimed.