Apple's iTunes and App Store restored their services after an unusually lengthy service outage that may have cost the company millions of dollars.

The service disruption, which lasted for roughly 12 hours beginning 5:00 a.m. ET, was caused by an internal technical error, Apple said. The disruption also affected Apple's iBooks and Mac App Store.

The outage was long enough to cause users to vent out their frustrations in not being able access the online content service and mobile apps store in Twitter, spawning hashtags such as #itunesdown and #appstoresdown.

"Customers may be unable to make purchases from the App Store, iTunes Store, iBooks Store, or Mac App Store," Apple said in a message posted on the company's status page.

It was not until 5:04 p.m. ET that Apple updated the company's status page to state that the disruption on the services has been fixed, with the error related to an internal Domain Name System issue.

Apple revealed that around the same time, the company's iCloud Mail and iCloud Account & Sign In services were affected. However, those services were restored after only four hours, by 9:00 a.m. ET.

iTunes and the App Store are integral to the mobile user experience offered by Apple's devices. In addition, the services are also important revenue sources for Apple, which is paid a certain portion of all the content purchased, including videos and music, and apps downloaded through the services.

Revenue from these services was almost $4.8 billion in the company's recently concluded fiscal first quarter, which represents 6 percent of the company's overall sales.

The average daily revenue that Apple makes from iTunes and the App Store is about $50 million, which means that such a half-day outage may have cost Apple lost revenues worth around $25 million.

"Based on 2014 iTunes Revenue: Apple is losing $34,246 per minute, $2,054,794 per hour the iTunes store is down," tweeted social media analyst Tim Grimes.

Apple issued a public apology to its users, but that was not enough to prevent a dip in share prices. The service disruption to iTunes and the App Store caused the price of Apple shares to decrease by 1.8 percent to $122.24 per share.

The service disruption comes just a few days after Apple's Spring Forward event, wherein the company unveiled the much-anticipated Apple Watch and the new 12-inch MacBook that features USB-C technology. The website of the Apple Store was temporarily shut down at the time, which is a customary practice for Apple before a major event.

"Service outages happen from time to time and we view this as a very minor event," said Daniel Ives, an analyst for FBR Capital Markets, to Reuters. 

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