"60 Minutes"/CBS News

Security experts say breaking into a smartphone is easier than you think -- and they've spied on a US Congressman's phone calls to prove it.

German computer engineer Karsten Nohl told "60 Minutes" in America that all a hacker needs is a phone number.

From there, Nohl says hackers can "track [the owner's] whereabouts, know where they go for work...spy on whom they call and what they say over the phone. And you can read their texts."

Just by knowing the number of an off-the-shelf iPhone and exploiting a known network flaw, Nohl was able to spy on Representative Ted Lieu of California (who agreed to participate in the demo) -- they then recorded his calls with "60 Minutes" and tracked his movements.

"Any choices that a congressman could've made, choosing a phone, choosing a pin number, installing or not installing certain apps, have no influence over what we are showing because this is targeting the mobile network."

Disclaimer: "60 Minutes" is owned by CBS, which owns CNET.