How has my phone been rooted?

[AC Question]

My husband recently upgraded his phone and it worked for about a week, then kept turning itself on and off. We took it into the Samsung store who said it had been rooted. We don't even know what this means (although I do now!!) let alone try and do it! Samsung wont fix it and neither will Vodafone so we don't know what to do as we cant prove we haven't done anything to it. Please help! THanks

 

[B. Diddy]

Welcome to Android Central! From where did you get the phone? Was it brand new, directly from the wireless store? Or was it from an online retailer, or some other independent electronics store? If it wasn't directly from the wireless store, I'd be suspicious that the seller wasn't actually selling you a "brand new" phone--it might have been used and returned.