Android OS background data usage Recently set up 2 Android smart phones for my sons earlier this month (around Dec 12th, 2015). On one of the phones, Android OS is showing a HUGE spike in background data usage. From Dec 12th until Dec 25th, Android OS used maybe 233MB of data. However from December 25th until 3 days later (December 28th - Yesterday) it suddenly used 4.30 GB of data!!! WTH?!?!

The family mobile data plan for each line is 6GB through T-Mobile. He was no where near the limit prior to Christmas. Suddenly POOF... over 4GB of mobile data used by the OS. WHY?? What happened? Did his phone get hacked? I have Kaspersky Internet Security installed on the phone since it was set up.. no alarms showing an issue. So what changed in the past 3 days??

The few apps installed barely account for any data usage. Yet Android OS is hogging it all. Is something lurking under that moniker?  Not happy one bit. See attached images for reference.
The same thing happened to me. 
While setting up Android there's an option for backing up all data to Google. It might be enabled on one of your sons phone. 
Goto settings ->backup &amp; restore 
Make sure "back up device data" is not checked. 
I did the same and it worked.