Comprehensive Guide to Twitter Privacy
I've become fascinated with how Twitter has such simple settings, and yet Twitter privacy is in many ways quite complex, so I'm starting to put all of this information together. This is part 2 of... a bunch.
[Part 1: Who hears what you say?]
[Part 2: Where are you?] <-- you are here!
Now read on to learn How your iPhone may be letting people know where you live and what being responsible about sharing your location really entails!
Part 2: Where are you?
A year ago, I talked about How Foursquare can help people steal your stuff. Someone had set up a handy site called PleaseRobMe.com which let you search to find out who in a given area wasn't at home based on their Foursquare checkins. (The site now says the the authors have made their point about oversharing and have disabled the search.)
The point being that while sharing your location can be a neat way to meet up with friends, it can also be used in dangerous ways. So whether it's Foursquare, Yelp, Facebook Places, Google Latitude, or Twitter, you need to think about what you're sharing and why.
Twitter's built-in location settings
At the time I wrote about PleaseRobMe.com, I don't think location was built into Twitter, but it's since been made an option for any Twitter post. I have to say, that I really love how twitter has done to make this option clear... including doing their best to make it possible to recover from an "oops" moment where you realise you've been sharing waaay too much information and want to delete all the location data to be safe:"Learn more" help document, which includes the following message:
Be cautious and careful about the amount of information you share online. There may be some updates where you want to share your location ("The parade is starting now." or "A truck just spilled delicious candy all over the roadway!"), and some updates where you want to keep your location private. Just like you might not want to tweet your home address, please be cautious in tweeting coordinates you don't want others to see.
That pretty much sums up the advice any security/privacy expert would give you, although the complete document also explains how to turn things on and off, when one might prefer a precise location and when one might prefer just the city, etc.
But just like with the tweet privacy settings we talked about in part 1, this isn't the only way your location can be shared. Only this time, we're not going to blame your followers... we're going to blame your camera.
How your iPhone may be telling everyone where you live
Many modern smartphones and cameras, including the iPhone, have a GPS built-in such that you can store location data with every photo. That's pretty cool when it comes to sorting photos later, but because this information is stored with a photo, each picture you share could potentially tell someone exactly where you are (or were when you took the photo).
In Cybercasing the Joint: On the Privacy Implications of Geo-Tagging, Friedland and Sommer started looking at how many people share location data, whether they did so in unsafe ways, and whether they were aware of what information they were sharing. I highly recommend you flip through their HotSec presentation to look at the examples. (Even better if you can catch them presenting -- I really enjoyed seeing that presentation in person! -- but the slides are pretty informative on their own.)
My favourite one involves William Shatner accidentally revealing a "secret" studio location when he posted about recording there! And perhaps more relevant to "cybercasing the joint" are the craigslist posts that show expensive items, their exact geolocation, and the list of times when someone will be at home to take a phone call from an interested buyer.
The issue here is that geodata is often recorded by default. And it can even be dangerous to share this information. As a parent, how would you feel if you realized your teenage daughter had been taking photos of herself in her bedroom and it turned out that any predator could figure out where she lived? How do you feel about the fact that your friends' photos from your last party may have told everyone on the internet where you live?
Many photo services, such as Twitpic and Flickr, allow you to generalize your data so that it shows up as being in a city without showing precisely where within that city. But if you choose to have it visible (or just don't hide the data), you can often get a nice map where you can zoom in:
On Flickr you can view the exif data (Exchangeable image file format -- basically extended meta-information for pictures of the photo) and get the coordinates there...
All ready for someone's stalking pleasure!
The moral of this story
Sharing your location can be scary, and protecting your location privacy doesn't stop at turning off location on Twitter or refusing to sign in to Foursquare/Facebook places/Yelp. If you don't want everyone to know exactly where you are, you also have to make sure your camera and your friends' cameras aren't giving the game away.
Stay tuned for more Twitter privacy posts in April! And in case you missed it, here's [Part 1: Who hears what you say?] which talks about tweet privacy.