Facebook has been the punching bag of the security and privacy advocates for ever. No wonder the movie on facebook, "The Social Effect" has the tag line "When you make 500 million friends, you are bound to make enemies". The biggest criticism for facebook has been that it knows too much about us and there are concerns about security and privacy of this data. Usual response to this criticism is that this is social media and if you are so concerned about privacy, don't share it. I was convinced with this argument until recently when I figured out, there are things which you don't explicitly share, but eventually reach facebook. Here is an example where you need to be aware that facebook is watching you. Many, won't know. I didn't.

Background
Recently, facebook introduced Social Plugins. These are facebook components that any website in the world could embed in their own webpage to provide social networking features through facebook. Examples are - "share on facebook", "like" button, friend list, comments, etc. This requires that the visitor has logged-in to facebook, may be through another browser window or tab. If a website ebmbeds the facebook "like" button on its webpage, the visitors of the website will be able click on "like" button (very similar to you like videos, photos, status messages etc on facebook itslef). This will result into an update on your Wall that you liked that link. This is good. I have no problems with this.
I have a problem with what it does next. Read on.

The Use Case
Follow the steps below.

1. Login to facebook.
2. Go to any article on Times Of India. Say this one.
3. Look at the bottom. You will see this facebook plugin - "Recommend".
   
   
4. If you observe closely, it also tells you if any of your friends have recommended this. In my case it says "Be the first of your friends to recommend this."

What happens in the background?
If you imagine the logic of this, the code snippet from facebook that TOI would have embedded in this page would have sent this info to facebook that amol has visited so and so URL, and in-return asked if anybody from amol's friends recommended this URL? In my case facebook returned none.
The Issue
This is scary. I just happened to be logged in to facebook in some another browser window and without even checking with me, the plugin sent the info to facebook that I visited Times of India - this article. I hate this. I didn't choose to add/enable this plugin to TOI. It did not check with me and peacefully sent the info to facebook that I visited this page. If you don't observe carefully, you would not even see the facebook plugin amidst the clutter on the site. Thankfully facebook didn't put it on my wall , but mind well... it knows that you visited it.
I do share a lot of info on facebook.com through my wall.... my status, photos, videos, links, etc. However, there I do it conciously.... by choice. Here, I never chose to do it. I don'thave option to turn it off either. Forget it, I didn't even know it did all this.
Simple Advise
Log off from facebook after you are done. Don't keep yourself logged in through out the day. Be aware that you are being watched.