Mobile security will be the next very big battleground. When everyone has a mobile phone that allows them to be tracked and spied on everywhere they go, this is already a problem. The phone knows where you are and where you've been, who you're talking to and what you're doing online. That information is already automatically gathered and sold by your phone company - it probably says so in your contract. So even if the operating systems of future mobiles are secure, there's a conflict of interest here. The mobile service providers need to know where you are to direct calls to you, and they need to know who you are talking to in order to direct the call to them. That data is valuable, so they have an incentive to retain and sell it. How do you fight back against a machine like that?
Mokalus of Borg
PS - That's more of a privacy concern, though.
PPS - But privacy requires good security.