If a user has publicly endorsed a product or service by clicking +1, or used rating or wrote reviews on products or services shared on other Google services, like the Play Store, then that information could be used too.
Even though Google+ users will be able to opt out, the changes to Google's terms of service policy has some privacy and digital rights activists speaking out.
"It's a huge privacy problem," said Marc Rotenberg, of privacy group EPIC, adding that Google users "shouldn't have to go back and restore their privacy defaults every time Google makes a change."
Rotenberg is suggesting that the U.S. Federal Trade Commission (FTC) review the policy change by Google, in case it violates a consent order Google entered into in 2011, barring it from retroactively changing the privacy settings of users.