Your hidden friends, betrayed by their like
Graph Search as a privacy tool
According to Facebook, Graph Search not only helps people finding information about their friends, it also helps them to know what information they reveal about themself. I find this objective questionable especially in France where many people are still not aware that Graph Search even exist  and yet have their profiles searchable by anyone in the US. Yet, Graph Search is certainly very useful and educative about what could go wrong with tagging and shared content.
The issue of the Friend List
When Facebook announced Graph Search in January, I was surprised by their decision to not show friends lists that could be recomposed by browsing timelines. Recomposing part of someone friends list was time consuming but possible if you spent time scrolling down the timeline.
Last July update of Graph Search makes it even simpler to retrieve list of friends of people who hide it. Indeed, Graph Search now allows you to search who liked or commented on photos. Since some content is only visible to my friends, only they can comment or like my pictures. Having a list of people who liked or commented on my photos is like having a list of my friends with who I share things on Facebook. Some people that I do not know commented on my photos, but that’s a negligible fraction.
Unwanted side effects
Surprisingly, it seems that you can even know if someone liked a photo you don’t have access to. Indeed, in some circumstances, you cannot see which picture has been liked; you only know that someone liked a picture (see bellow).
It goes against Facebook claim that Graph Search only gives you access to information you already had.
Update: In fact, the person who liked the picture is not searchable but she appears in the search results because she liked a public photo.
Another annoying effect is that queries like “People who liked photos by me” returns a list of people with who I’m no longer friend. And it’s pretty easy to spot these people because they are systematically at the end of the result list.
How bad is it?
To measure the fraction of the friend list that could be retrieved through Graph Search, I listed the number of results that were listed when I search for:
- Q1 :“People who liked photos by X”
- Q2:“People who commented on photos by X”
- Q3:”People who uploaded photos liked by X”
- Q4: “People who uploaded photos of X”
Unfortunately, Graph Search does not (yet?) support ‘OR’ queries so there is no easy way to quantify the overlap between these four queries . I reported numbers of confirmed retrieved friends (using the “mutual friend” filter) and the total number of retrieved people because it also includes former friends. I compare that to the number of friends I have (and I thank my friends who did not hide their friends list).
|59 ( 73)
I made some tests on a few friends and I obtained similar results , queries Q1 and Q3 are the more effective queries in general. On average, Graph Search returns 30% of friends, plus some former friends. I guess I could retrieve up to 40-50% by combining the four queries. It’s problematic because many people assume that their friend’s lists are safe, but this safety goes away when they share likable photos or when they like photos.
Since “Like” visibility is public, you can even retrieve some friends of people with who you have no connection. I can imagine many circumstances where having your list of friends publicly available is very problematic.
What can you do?
Unfortunately, you cannot prevent your friends from liking content you share with them. Likes are not like tag or comments: they cannot be removed. The only current solution is to not share “likeable” content or to ask to people to not like it, but that’s very counter intuitive on Facebook. In the end, you can only hide friends who don’t “like” you.
Another solution is to obfuscate the list of people who liked your pictures. I probably rely too much on obfuscation, but asking people you don’t know to like your photos is currently the only technical solution to prevent stalkers from quickly retrieving your friends.
Acknowledgements: Thanks to my stalked friends who do not share their friends lists, they motivated this post. Thanks to those who do share their list, they helped me to make this post relevant.
 If you have not yet enabled “Graph Search”, I recommand you to do so. See http://www.fredzone.org/comment-activer-le-graph-search-de-facebook-929
 I’ll post more results when I’ll get their consent