And what about iPhone4? Are the leaks in iOS7 as well?

Apple advises you stay current with the patches for iOS as it address the latest known security issues. If an apple device is no longer supported your security is only as good as the what was included in the last iteration of an OS that device supported.

Look here:

https://citizenlab.org/2016/08/million-dollar-dissident-iphone-zero-day-nso-grou p-uae/

Says the exploit started in ios 7.x.

Says you need to visit an malicious web site.

Says you can/may be able to tell if you got it.

Says the exploit costs $1million to purchase for 800 licenses. One would guess the price would come down now that the cat is out of the bag.

R