Google changed its privacy policy in June to allow for the tracking of personally identifiable data.

Under the opt-in feature, a users' personally identifiable information is merged with their browsing record from all over the internet. The company had earlier promised to keep these sets of data separate to protect users' privacy.

According to Propublica, Google updated its privacy policy earlier this year and deleted a clause related to the tracking of personally identifiable information. The clause stated, "we will not combine DoubleClick cookie information with personally identifiable information unless we have your opt-in consent." However, the change was largely ignored by users and the media.

Since the feature is opt-in, existing Google users were coaxed to do so with requests such as "Some new features for your Google account." New Google accounts come with automatic opt-in for this elevated level of data sharing. The company told Propublica that the changes were carried out to make the service more smartphone friendly. It said that with the new policy, the users would get to see ads which are more relevant to them.

Facebook can already track its logged in users when they choose to share items from other websites. Twitter follows the same policy. Facebook can track the users by their names when they access any website with Facebook buttons including 'Like' and 'share.'

Users can opt-out of this feature by going to My Account page on Google and accessing Activity controls. Users may also choose to delete their past data from their accounts.