Do not auto-mount Samsung Galaxy S4 Mini when USB is connected I had an HTC desire phone, before upgrading to a Galaxy S4 Mini. 

I have run into an annoying problem. On my phone (not on the SD Card), I have private data, including an RSA key, which I use to SSH into my different computers and servers. On the Desire S, I had the phone on default "Charge only" so people who nicked my phone didn't just get access to what was on it.

How do I do something similar with the Galaxy S4? I need some way to disable the mount-by-default so people who steal my phone can't just plug-in a USB cable and steal all my data. The phone should still be able to mount as a storage device, but ONLY when it is specifically activated.

In screen-locked mode, it still auto-mounts when plugged in - not exactly a good way to protect the data on the device.
I don't know if this applies to the S4 but on my Nexus devices it shows up on my pc as a 'drive' but I can't access anything until the phone is unlocked (the normal screen lock - pattern/pin). If you have a screen lock set it shouldn't allow access to the device until you unlock it.