Although Windows 10 has gotten off to a great start by pretty much any metric, Microsoft’s mobile version of Windows 10 has had a pretty bumpy road. Originally thought to be an update for current phones sometime late last year, Windows 10 Mobile is still not available unless you purchase a new Lumia 950, 950 XL, or the budget Lumia 550, all of which were announced in October in New York City along with the Surface Pro 4 and Surface Book.

That does not preclude people from using the new mobile operating system on their existing handsets, because Microsoft offers people in the Windows Insider program access to the pre-release software. Windows 10 Mobile is available for quite a few Lumia handsets, as well as a couple of others like the HTC One M8 for Windows.

For those either with one of the newer Lumia phones, or if you are running on the pre-release version of Windows 10 Mobile on an existing handset, one nasty bug caught me out this month. Windows 10 Mobile includes Data Sense, which originally came back with Windows Phone 8.1, and this system tool monitors all network traffic and reports back usage over WiFi and Cellular. On my own Lumia 950 XL, I noticed I had used more cellular data in January than I had ever used in a single month before. Data Sense let me know that a process called “System” had used over 900 MB of cellular data in just 17 days. Beautifully vague as all bugs are.

Speaking with some other people that use Windows 10 Mobile, I found that it was not an isolated incident. Other users had been reporting the same issue, and in some cases they had used quite a bit more data than this. The culprit, it seems, is a setting which is on by default that backs up text messages to OneDrive, so that you can get them back if you get a new phone or wipe your current phone. It’s a feature that has been part of Windows Phone for some time, and I’ve always left it enabled. Disabling this setting reduces the cellular data usage back to normal. In the messaging app main window, hit the … in the bottom right corner, choose Settings, and turn off Message Sync. To be clear, backing up the text messages should only use a small amount of data, and really it should do it over WiFi only. This is a feature I will re-enable when the bug is resolved.


System used 909 MB on Cellular and 2.79 GB on WiFI in 17 days

In addition, Windows 10 Mobile offers a new feature which will back up install apps to OneDrive as well, and that can be disabled too since it may also contribute to cellular data usage, even if things like the Store are set to download updates only over WiFi. This setting is found under Backup settings.

I reached out to Microsoft to see if they were aware of this issue. In the current age of mobile data caps, this can and has caught people out, causing them to have to pay overage charges with their cellular providers. A Microsoft spokesperson said:

“We have received some customer feedback regarding unexpected mobile data usage and are looking into this.”

The fix provided here is unofficial, in that it hasn’t come directly from Microsoft PR but rather through a Microsoft employee on Reddit thread found by Paul Thurrott of, but it has appeared to fix the issue I was having. In the last 24 hours, my System process has only used 0.5 MB of data. If you are running Windows 10 Mobile, I would suggest you check into this to avoid racking up any charges on your bill.

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  • steven75 - Thursday, January 28, 2016 - link

    These are all public companies, so it is trivial for anyone to look up the respective company's quarterly reports and confirm the fact that Google is the only one that bases their business model on "seling your data to anyone that can pay".
  • BrokenCrayons - Thursday, January 28, 2016 - link

    The people upset about Google's various questionable practices have a new company to victimize in Microsoft because MS previously was using its lack of data mining and telemetry collection as a selling point in their advertisements. I personally think that Microsoft is only just catching up to Google so the change is more obvious and more upsetting than what Google was and still is doing because the passage of time has made us insensitive to Google's data harvesting efforts.
  • xthetenth - Thursday, January 28, 2016 - link

    Yeah, it's disappointing, although from their claims MS at least tries to anonymize your data, something Google pointedly doesn't do.
  • JonnyDough - Monday, February 1, 2016 - link

    "Catching up", makes it sound like they were behind. They weren't behind, they were more advanced. Now they've thrown in the towel and stooped to Google's level.
  • SpartanJet - Wednesday, January 27, 2016 - link

    Its funny that both apple and that ad company both have had issues like this in the past (even recently with iOS 9 and Wi-Fi assist) but it wasn't worthy of a headline i guess.
  • jiffylube1024 - Thursday, January 28, 2016 - link

    Riight. It's this kind of conspiratorial thinking that always befuddles me. iOS 9 data leaks were a big deal at the time, before they got fixed:
  • SpartanJet - Thursday, January 28, 2016 - link

    Riiight. Gee I wasn't talking about every single news source, I was talking about here on Anandtech. Nice try though.
  • name99 - Thursday, January 28, 2016 - link

    Swing and a miss on Apple...
    The WiFi assist issue seems to be nonsense, basically a scam by some lawyer hoping to gin up a case.
    What makes your claim so absurd and so ignorant is that there IS an Apple cellular data usage. On at least two occasions within the last three months, something has gone wrong on the iCloud backend resulting in it generating an excessive number of document synchronization requests with iOS, and if you're on cellular, that ramps up your cellular usage. Not by these MS amounts, but by around 5..10MB an hour, which can add up if you have a 200/300MB plan, or even a 2GB plan and are always outside. But this hasn't been publicized much.
  • Ruimanalmeida - Wednesday, January 27, 2016 - link

    Hi, This backup capability to OneDrive (apps+settings+text messages+photos+videos) is already available at Win Phone 8.1 Update OS, so it is not specific from Win 10 Mobile.
  • Murloc - Thursday, January 28, 2016 - link

    the bug is.

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