I don't know how new these tricks are -- I don't log in to Facebook very often -- but today I noticed a nifty new feature that makes it even easier to find out information about people that they might not want you to find. I've already used it to track down the identities of some formerly-anonymous SFist tipsters.
Here's how it works: Facebook asks you for your email address and password. It looks like a pretty useful, safe feature -- once you supply your details, Facebook runs through your address book and figures out if anyone you've ever emailed -- even once -- has also used that email address on Facebook. Then it says, "hey, this person you once emailed, they're on this site! You could be Facebook friendsters!" It doesn't save your login info, and it doesn't email anyone without your permission.
This is pretty handy, and I've used it to get in touch with some friends on Facebook whose email addresses I'd forgotten I had. But I was surprised to see some names I didn't recognize: they were people who'd emailed me anonymously with tips for SFist. I hadn't been able to get any info about them any other social networking site; their names weren't attached to the emails, and they hadn't used that email address on any other social networking websites. But for some reason, more than one source had used for Facebook the same email address that they used to write to me.
So, for example, Facebook was showing me the first name and last name that "S," who wrote to me about Google. With that info, I could easily find him on MySpace and Friendster and even verified his employment. I also found out that a local news anchorman, who'd emailed me about a story I did about buses, has a Facebook profile of his own. I bet, when these folks sent me an email, they never stopped to think, "now, I wonder how this will impact my visibility on Facebook."
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