After receiving calls from my data provider of over usage of more than 3gb within 1 hour even though I was not even using iPhone , instead I was using internet on my personal computer which was connected to my home internet connection ( bell) via home wifi router . The data usage stats on iphone showed that personal hotspot has used all the 4.5gb of data. And this incident has occurred 2 days in a row now.... Here is what I think is happening with my iPhone6 data usage problem. When I am at home , my Iphone6 automatically connects to my hone internet ( e,g bell) via wifi .because wifi settings is enabled on my iphone and my home internet is a know network for iPhone ... And When I leave my personal hotspot enabled on iPhone then my Iphone acts like a router meaning whenever i am using internet on my home computer even though my home computer shows it is connected to my home bell internet via home router but it still uses my iphone cellular data( telus) .because my iphone is also connected to same internet via wifi . The above is the only explanation I can come up with what is happening . I used the above settings with Iphone4 iOS5 for years but this problem never happened. So either this is a feature of iphone6/iOS8 or a bug. The million dollar question here is that how dare the home computer able to use iPhone data when NO personal hotspot password ever has been entered on the computer and never any attempt been made to connect to Iphone from my home computer. With all the above situation , the automatically connecting feature of iphone for known wifi connection is dangerous .... Apple must comeup with the feature to give the option in settings so that it can also be set as "always prompt for the password" for known wifi networks.