It looks as though the algorithm used to generate iTunes Store gift cards may have been cracked.
iTunes Store gift cards are on sale on Chinese websites, such as Taobao, for as little as £4.25 for a $200 (£145) voucher.
Reports from Gizmodo suggest that the voucher numbers are being generated by Chinese hackers who have reverse engineered the algorithm and are selling $200 keys to vendors on Taobao.
Taobao is a consumer-to-consumer retail website in China, in which Yahoo! holds a 40 per cent stake.
The cracked $200 gift card keys are now starting to show up on eBay in the UK, although prices are still a little higher.
iTunes vouchers can be used to redeem the full range of products at the Apple Store including music, video and game downloads, and iPhone appplications at the App Store.
There has been no official comment as yet from Apple.