How does Facebook "know" Other People You May Know?

OK, so this is freaking me out a little, and I’m curious if anyone has any ideas how FB does this:

To begin with, I am an extremely cautious and private closet crossdresser. (TMI, I know, but stick with me); at most I have a Flickr account with private photos which are not shared and my personal email account.

I also used to play Second Life religiously as a female avatar, and only two people ever knew I wasn’t female in real life. I kept a blog, but my gender and real identity were never in any way connected with that avatar name.

So basically what I’m saying is that I’ve been extremely cautious for many many years in making sure my name (“alias”?) when crossdressed and my avatar name have never been related in any way to my male name.

For my normal male identity I have an active FB account which I check regularly.

When I was still active in Second Life, I would occasionally get those “Join Facebook” invitations from friends which include people I might also know to entice me to join. It freaked me out that my actual male identity with my profile picture appeared in those emails! Because I found this so tremendously creepy, I always resisted joining FB with either of my alternative identities.

Today, I succumbed to temptation and opened a FB account with my crossdressed identity. To be as secure as possible, I used a VPN to hide my IP address and used the Incognito mode in Chrome to hide my identity from FB. Obviously I used a different email address and no other identifying information. I even cropped my profile pic to just my eye, in case FB was using some sort of facial identification.

So I open up my new Facebook page with people I may know, and what do I find? Facebook suggests my male identity as someone I may like to be friends with.

WTF?! SOMEONE PLEASE GET ZUCKERBERG OUT OF MY DAMN HEAD!!!

I don’t know how Facebook’s algorithm works, but the most obvious way to do something like this would be to look at friends in common. Did both of your identities have some common friends? (Note that they might not be reciprocal resationships; it might be enough that someone else added both of your identities as friends, or attempted to; they might even be further removed than that).

I’m just speculating, as I expect this is a closely guarded secret. But I doubt it has anything to do with tracking you via IPs, your computer, cookies or the like - that sort of thing is too unreliable at large scales. Much more likely they’re analysing what you do on Facebook, and looking for other accounts that do similar things.

The Suggested Friends works by both looking at what people your friends have friended and have similar interests or locations, and by whether one of your registered email addresses was found when one of your friends used the Friend Finder. The Friend Finder looks through the user’s email account for email addresses that correspond to current Facebook users. Of all the people that show up on my suggested friends, only old consulting clients are ones I have exchanged email with. The others are friends of other friends who live in the same areas as me and attend the same schools.

Note that Incognito mode in Chrome, private browsing in Firefox, or InPrivate in IE do not and are not intended to hide your identity from the sites you browse to. They are designed only to prevent other users of your computer from discovering what sites you visited with it on. There’s a reason it’s called “porn mode.”

Oh good lord. I shot myself in the foot then. Rather stupidly, I have email addresses for both of my other identities as a once-used email address in my male gmail contact list. When I signed up for FB originally, I did use the contact scan function.

Well, that’s one mystery solved. Google and Facebook were smarter than me. :confused:

Thanks!