According to the lawsuit, Facebook looks at messages containing hyperlinks, follows the link and profiles the web activity of the user. If it finds a link to a website that also has Facebook’s social plugin, Facebook registers up to two Likes for the web page via the social media plugin.
This behaviour violates the Electronic Communications Privacy act and the California Unfair Competition Law (“UCL”).
But you gave Facebook permission to use your data when you signed up for the account…
“For content that is covered by intellectual property rights, like photos and videos (IP content), you specifically give us the following permission, subject to your privacy and application settings:
You grant us a non-exclusive, transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook (IP License).”
By "content" Facebook means “anything you or other users post on Facebook”. By "information" Facebook means “facts and other information about you, including actions taken by users and non-users who interact with Facebook”.
In signing up for a Facebook account, you have effectively permitted Facebook to use any data you enter on the site for anything it wants to.
And Facebook is not the only company to do this.
Google reads your emails
When you sign up for a Gmail account you allow Google free use of anything you write to the site. Google can do basically anything it wants to do with your content. You agreed to its Terms of Service when you created the account.
This applies to other Google services such as Picassa, Google docs, YouTube or Google+. You have granted Google similar rights over that content just by using its services.
When you upload or otherwise submit content to our Services, you give Google (and those we work with) a worldwide licence to use, … reproduce, modify, create derivative works (…. adaptations or other changes that we make so that your content works better with our Services), …, publish, …, publicly display and distribute such content.
The rights that you grant in this licence are for the limited purpose of operating, promoting and improving our Services, and to develop new ones.
(A) clicking to accept or agree to the Terms, … for any Service; or
(B) by actually using the Services. …, you understand and agree that Google will treat your use of the Services as acceptance of the Terms from that point onwards.
Google searches and ads
In September a judge ruled that Google must face a suit in relation to Gmail message scanning. Google said it automatically scans emails to target advertising based on words that appear in Gmail messages but says that machines, not people, do the scanning.
Ultimately if you want to use a free service, you have to pay the costs to run that service somehow. Advertising and marketing funds the ‘free’ services we use every day.
Only you can decide if Facebook accessing your private messages is too high a price to pay.