Apple makes it easy for people to locate lost iPhones, share Wi-Fi passwords, and use AirDrop to send files to other nearby devices. A recently published report demonstrates how snoops can capitalize on these features to scoop up a wealth of potentially sensitive data that in some cases includes phone numbers.

Simply having Bluetooth turned on broadcasts a host of device details, including its name, whether it's in use, if Wi-Fi is turned on, the OS version it's running, and information about the battery. More concerning: using AirDrop or Wi-Fi password sharing broadcasts a partial cryptographic hash that can easily be converted into an iPhone's complete phone number. The information - which in the case of a Mac also includes a static MAC address that can be used as a unique identifier - is sent in Bluetooth Low Energy packets.

The information disclosed may not be a big deal in many settings, such as work places where everyone knows everyone anyway. The exposure may be creepier in public places, such as a subway, a bar, or a department store, where anyone with some low-cost hardware and a little know-how can collect the details of all Apple devices that have BLE turned on. The data could also be a boon to companies that track customers as they move through retail outlets. As noted above, in the event someone is using AirDrop to share a file or image, they're broadcasting a partial SHA256 hash of their phone number. In the event Wi-Fi password sharing is in use, the device is sending partial SHA256 hashes of its phone number, the user's email address, and the user's Apple ID. While only the first three bytes of the hash are broadcast, researchers with security firm Hexway (which published the research) say those bytes provide enough information to recover the full phone number.

Hexway's report includes proof-of-concept software that demonstrates the information broadcast. Errata Security CEO Rob Graham installed the proof-of-concept on a laptop that was equipped with a wireless packet sniffer dongle, and within a minute or two he captured details of more than a dozen iPhones and Apple Watches that were within radio range of the bar where he was working