Xcode process launch failed: Security
If you get this, the app has installed on your device. You have to tap the icon. It will ask you if you really want to run it. Say “yes” and then Build & Run again.
As from iOS 9, it is required to go to Settings → General → Device Management → Developer App → Trust`.
On some versions of iOS, you will have to go to Settings → General → Profile instead.
Updated answer for Xcode 7: Tapping the app no longer works (as of beta 1 it just displays an "untrusted enterprise developer" message with only a Dismiss button).
To fix, open the Settings app, go to General / Profiles, and you'll see your profile. Mark it trusted and things should start working normally again.
Updated For iOS 9.2.1 and Xcode 7.2.1:
Goto: Settings > General > Device Management > Select App from Developer Apps > Trust App.
Hey so the accepted answer works, except if you need to debug the initial launch of the app. However I think that answer is more of a work around, and not an actual solution. From my understanding this message occurs when you have some weirdness in your provisioning profile / cert setup so make extra sure everything is in tip-top shape in that dept. before ramming your head against the wall repeatedly.
What worked for me was as follows from the apple docs:
Provisioning Profiles Known Issue If you have upgraded to the GM seedfrom other betas you may see your apps crashing due to provisioningprofile issues.
Workaround:
Connect the device via USB to your Mac
Launch Xcode Choose Window ->Devices
Right click on the device in left column, choose "ShowProvisioning Profiles"
Click on the provisioning profile in question
Press the "-" button Continue to removing all affected profiles.
Re-install the app
Make sure you right click on the image of the device not the name of the device or you won't see the provisioning profiles option. I restored my new phone from an old backup and there was a lot of cruft hanging around, i also had 2 different dev. certs active (not sure why) but i deleted one, made a new profile got rid of all the profiles on device and it worked.
Hope this helps someone else.