When turned on wi -fi something unknown uses data suddenly When i turned on wi-fi something unknown uses data rapidly..I use android version 4.4.2 ..Can't find anything that uses data, I did a virus scan, and removed all unknown apps also,and there are just a few apps,I've installed..Does it use by the OS or other thing,I tried to run only with mobile data but some apps ask for wi-fi..How can stop this unknown data usage, without turning off wi-fi..
Yes i found the answer..
settings-> about phone -> tap build number for few times(that enables developer tools..)

settings -> developer tools -> background processes limit -> no background process 

that's all..Now data usage while phone is idle is 0..