iPhone 3- Was set up with someone elses iTunes account, are they able to access my phone?
Find My iPhone can be instructed to remotely wipe an iOS device, if that service was enabled on your phone.

It can also be used to track the location of a device, which you should also be concerned about.  However, once the device is erased, it can no longer be tracked.

Further reading: iCloud: Erase your device remotely