told advertisers in a blog post Wednesday that it’s been und...

$Facebook(FB.US)$ told advertisers in a blog post Wednesday that it’s been underreporting ad performance on $Apple(AAPL.US)$ iPhones, citing changes to the iOS operating system. Facebook estimated it is underreporting web conversions on Apple’s iOS by about 15%. Apple’s update made it so that iPhone and iPad users would have to choose to opt in to being tracked when first launching an app.