One of my iPhones went missing yesterday from my car parked outside my wife's shop (unlocked). Noticed it gone and started looking for it by calling it from other iPhones and checking the Find My Phone app, no luck. Gone for about an hour and a half it mysteriously reappeared in my wife's car parked next to where my car had been parked when the phone went missing (also unlocked). While it was gone it called itself 3 times and apparently the FMP app had been disabled then turned back on before it was returned. Just being paranoid or should I be concerned about security?
The SIM can be cloned rather easily, albeit illegally. This effectively creates another copy of your Subscriber Identity Module, and therefore creates a duplicate "phone". The contents of the device need not be viewed/copied/cloned and may or may not be duplicated on the new device, but the subscriber identity - which is the phone number, etc - can be cloned onto a new SIM, and used to affect your usage and billing.
Incidentally, the cloned SIM can be used in any device in which a SIM can be used - it need not be used in an iPhone... so effectively you can "clone" your iPhone onto an android device, for example.
While the process is not that common, and is absolutely illegal in the US, it is not entirely unheard of.