"Untrusted App Developer" message when installing enterprise iOS Application

I'm developing an enterprise application. When I was testing it in iOS8 beta I saw the following alert view:

Untrusted App Developer
Do you trust the developer "iPhone Distribution: ---" to run apps on you iPad?

It only appears the first time. Can I avoid it somehow? And what is it related to?

Today, I was testing this with iOS 9 Beta and found the solution.

To solve it, go to:

1. Settings -> General -> Profiles [Device Management on iOS 10]
2. Under ENTERPRISE APP, choose your current developer account name.
3. Tap Trust "Your developer account name"
4. Tap "Trust" in pop up.
5. Done

You cannot avoid this unless you distribute an application via the App Store.

You get this message because the application is signed via an enterprise certificate that has not yet been trusted by the user. Apple force this prompt to appear because the application that is being installed hasn't gone through the App Store review process so is technically untrusted.

Once the user has accepted the prompt, the certificate will be marked as trusted and the application can be installed (along with any other future applications that you wish to install that have been signed with the same certificate)

Note: As pointed out in the comments, as of iOS 8, uninstalling all applications from a specific certificate will cause the prompt to be shown again once an application from said certificate is re-installed.

Here is the link to Apple website that confirms this info: https://support.apple.com/en-us/HT204460

On iOS 9:

Settings -> General -> Device Management -> Developer app / your Apple ID -> Add/remove trust there

This issue comes when trust verification of app fails.

You can trust app from Settings shown in below images.

If this dosen't work then delete app and re-install it.

In my case, i just change some step below with iOS 9.3 To solve this problem:

Settings -> General -> Device Management -> Developer app Choose your current developer account name. Taps Trust "Your developer account name" Taps "Trust" in pop up. Done

You absolutely can avoid this issue if you manage the device with MDM or have access to Apple Configurator.

The solution is to push either the Developer or iOS Distribution certificate to the device via MDM or Apple Configurator. Once you do that, any application signed by that cert will be trusted.

When you click on "Do you trust this developer", you're essentially adding that certificate manually on a per-app basis.

If you push it out through MDM it should auto-trust the application (https://support.apple.com/en-gb/HT204460), but it still has to verify the certs etc with Apple to ensure they've not been revoked etc i presume. I had this message preventing the application from launching and it was only when the proxy information was configured so it i could use the internet that it went away after a couple more launch attempts.

In iOS 9.1 and lower, go to Settings - General - Profiles - tap on your Profile - tap on Trust button.

In iOS 9.3.1 and up: Settings > General > Device Management

For iOS 13.6

Go to settings -> General -> Device Management -> Click on Trust « Apple Development » -> Click on the red trust button and you’re all set!  Enjoy