UPDATE 5:30pm (GMT): Apple has issued the following statement, blaming the ongoing issue on a DNS error:
"We apologize to our customers experiencing problems with iTunes and other services this morning. The cause was an internal DNS error at Apple. We're working to make all of the services available to customers as soon as possible, and we thank everyone for their patience."
A global failure of its iTunes, App and iBook stores has cost Apple at least £10 million in revenue, as iPhone and iPad users in over 40 countries are unable to buy apps, games, music and films.
Hundreds of millions of Mac, iPod, iPhone and iPad users around the world have been unable to properly access and download content from iTunes, iBooks and the App Stores for both iOS for several hours. At the time of publication (5:30pm, GMT), the services remain offline.
It has also been reported that Apple Stores have resorted to processing card payments manually, due to in-store card machines no longer working; store Wi-Fi has also been knocked offline, although it is not clear if these two issues are related to the iOS and Mac store woes.
For its first-quarter financial results, published on 27 January, Apple reported $4.8 billion (£3.2bn) revenue for its 'Services' division, which includes the iTunes Store, App Store, Mac App Store, iBooks Store, AppleCare and Apple Pay; the last two are not believed to be affected by the outage.
Converted to £3.2bn, we have then divided this by 12 weeks in a three month quarter, then seven days and 24 hours to reach £1.6m revenue per hour.
But this figure could have been an awful lot higher. The App Store set a new weekly revenue record in the first seven days of 2015, reaching "nearly half a billion dollars." If Apple suffered a similarly crippling store outage during that period, the revenue loss could have been as high as $3m (£2m) per hour before factoring in any revenue from iTunes music, TV and film.
Apple takes a 30% cut from the revenue of all content sold through the App Store, with the remaining 70% going to app developers. Based on that record-breaking week, Apple gives developers up to £1.4m per hour.
The latest update at 5.30pm (GMT) on Wednesday from Apple said that the issue with iTunes, iBooks Store, Mac App Store and the iOS App Store is on-going and affecting all users. As of last August the company had 800 million iTunes accounts which gives an indication as to the size of the problem.
According to the website Down Detector, the first reports of issues with iTunes were reported at around 9am (GMT) on Wednesday morning (11 March) with most problems occurring in Europe and the US.
Apple said that iCloud account and sign-in problems affected all its users, which again numbers into the hundreds of millions of users - but this was fixed shortly before 1pm GMT on Wednesday). Apple's iCloud Mail service was also down for a period of time and affected all users, but Apple claims this is now also fixed.