Please Educate Me : Mobile phone security...
 

http://i.imgur.com/fY5dRjz.jpg

I'm not a big phone user, and I have a Galaxy Ace thats pretty old now, so I'm looking at a second hand / pre-owned Samsung Galaxy S4. The question is, that buying second hand / used how can I be sure there isn't any hidden spyware installed on it, that would send my passwords, messages, bank details etc to some third party?

If the answer is 'I cant...' thats fair enough.

Thanks :)

Do a factory reset after you buy it.

Would that kill ALL known spyware? Or just the ones you can get online easily?

As far as I know it will restore it to factory settings, essentially the same as doing a clean install of windows on a pc. All the updates since the phone was made will be downloaded again since you've basically wiped it clean.

Thanks :)