Updated at 1:26PM Pacific with Apple confirmation of the HealthKit bug.

Apple has now confirmed the existence of a bug in HealthKit: “We discovered a bug that prevents us from making HealthKit apps available on iOS 8 today,” the company says in a statement. “We’re working quickly to have the bug fixed in a software update and have HealthKit apps available by the end of the month.”

Hundreds of developers have been working on health apps that tap into data collected on Apple’s HealthKit platform. They expected to be able to launch their apps today with the release of iOS 8, but Apple earlier alerted app developers that it’s putting their apps on hold.

VentureBeat heard from several app developers in this boat, and one says it had been contacted by Apple about problems with the launch.

WebMD was set to launch a new HealthKit-connected app called Healthy Target today. “Our new app had been available for download in the app store until 10:30 this morning, at which point it became unavailable,” WebMD spokesman Adam Grossberg said in a note to VentureBeat. “We have been in contact with Apple about this issue, and expect to see the previous version of our app (v 5.2) back in the store on a temporary basis.”

Carrot Fit’s creator Brian Mueller was one of the first to tweet out the problem early Wednesday. “I can confirm that CARROT Fit was pulled from sale, and I’m working on resubmitting an older version that will go up on a temporary basis until Apple can correct the problems they’re seeing with HealthKit,” Mueller said in an email to VentureBeat.

Some developers on Twitter have attributed the problems to data management issues on the HealthKit platform. But for Apple to keep HealthKit completely under wraps for what could be a month, the problem would have had to be a big one. It’s possible that “bugs” might mean problems with the way Apple intends to keep HealthKit data private and secure.

HealthKit is a key part of Apple’s latest mobile operating system, which went live today. HealthKit collects personal health data from devices like watches and connected scales and combines the information in iOS 8’s new Health app. Developers can also access this data from the HealthKit platform.

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