Smartphone battery levels are being exploited to track users online, new research shows.
An API in HTML 5 enables sites to deliver low-power pages to mobile users of Chrome, Firefox and Opera who are short on battery.
But leading privacy advocates warned last year that the feature could be used for ulterior purposes. Now their fears have been confirmed.
Normally, when a user clears their cookies, a monitoring web script will see them as a new user.
But the battery status API in HTML 5 offers websites and adverts data about a users’ battery in both percentages and seconds, providing an identifier of individual phones.
Therefore, a script could link the “new user” to the known user through their battery data and continue to track them.
A year ago, researcher Lukasz Olejnik warned that the API could be used for this purpose. Two researchers at Princeton University have now proved that it has been.
Using a modified browser, Steve Engelhard and Arvind Narayan discovered two tracking scripts that used the API to identify devices, the Guardian reports.
Olejnik’s original research led Firefox to issue a fix and W3C, the international standards organisation for the web, to update their standard to reflect the analysis.
But the Princeton study will alarm privacy advocates who believe users should be able to search the web without being followed.
In a blog on the topic, Olejnik wrote: “Expected or not, battery readout is actually being used by tracking scripts, as reported in a recent study. Some tracking/analysis scripts (example here) are accessing and recovering this information.”
Olejnik also warns that the data could be used by companies to encourage users to pay more for some services when there phone is about to run out of battery.
Some browser vendors are now considering restricting and removing access to battery readout mechanisms, according to Olejnik’s blog.
The best smartphones of 2016
The iPhone 6s
on the surface at least looks like your bog standard update. Visually it's very much the same animal but look a little deeper and this is an entirely different phone. There's now a pressure-sensitive display utilising a feature called 'Force Touch' while a blistering new processor means it's one of the most capable gaming devices outside of your living room.
The new HTC 10
might not have the waterproof credentials of the Galaxy S7 but what it lacks in weather resistance it more than makes up for in media specs. This is a Hi-Res audio playing pro thanks to dual-amplifiers built-in and Hi-Res audio headphones provided as standard. It also has one of the best screens we've ever seen on a smartphone, so there's that.
Incredibly, Apple's familiar-looking iPhone SE
manages to boast the same performance as its top-of-the-range iPhone 6s making it the most powerful 4-inch smartphone available. If you're keen to return to the days of one-handed texting then Apple's bite-sized iPhone is the smartphone for you.
Bloomberg via Getty Images
With a new curved back and larger 5.5-inch display the Samsung Galaxy S7 edge
is more about evolution than revolution. The S7 edge now sports a water-resistant body, embedded camera and a MicroSD card slot. The S7 edge is also Samsung's most powerful smartphone yet, so powerful in fact that Samsung have actually had to equip a tiny water-cooling system inside the phone. The good news though is that means you'll never have to worry about getting a warm hand.
The LG G5
sets itself apart from rivals like the S7, Xperia XA and the iPhone 6s by being something utterly unique. The G5 is the first commercial 'modular' phone, allowing you to swap out the bottom for new accessories. So far there's an audio one made in partnership with Bang & Olufsen and a camera-focused attachment which gives you extra camera controls.
JACK TAYLOR via Getty Images
The Huawei P9 is a smartphone designed for capturing life. Thanks to a partnership with photography legends Leica this dual-lens camera can take pictures that'll put your dedicated camera to shame. Of course it helps that the P9 is also a pretty great Android smartphone as well.
The Nexus 5X
strikes the ultimate balance between power and affordability. Taking over the responsibility from the frankly excellent Nexus 5, Google's new smartphone boast an ultra-light body but still crams in a fingerprint sensor, the latest version of Android marshmallow and a Full-HD display.
Sony has created the world's first truly 4K smartphone
. While you might be wondering why, the fact is they've gone ahead and done it anyway. Utilising Sony's amazing screen expertise it should come as no surprise to learn the display is an absolute stunner. There's a fingerprint reader and the ability to play high-res audio.
The Google Nexus 6P
is Google's answer to the big-screen phone. Sporting a 5.7-inch Full-HD panel, the 6P has a beautifully thin unibody enclosure while the subtle fingerprint scanner on the back can be used for security and for paying. You'll also get the added advantage of owning a phone that'll always get Google's Android software before anyone else keeping it safer than ever.
The Moto X Force might not be the most stylish phone of the bunch but what it lacks in looks it more than makes up for in strength. With an 'unbreakable' screen the Force is a no compromises Android phone that has a 5.4-inch AMOLED display.
The OnePlus 2 describes itself as the 'Flagship Killer'. It's a bold statement for a company that has made just two smartphones. Despite this the OnePlus 2 lives up to its name, for just £249 you get a stunning Android smartphone that boasts a huge display, large storage and a fingerprint sensor. It's also pretty much customisable to within an inch of its life so if there's anything you don't like about Google's operating system, well you can change it.