Security researcher Joe Stewart believes this is the work of credit card thieves looking for a place to turn stolen data into raw cash. Either the Chinese hackers have managed to penetrate Apple s internal network and/or iTunes gift card database, or they are simply using stolen credit card numbers to purchase the cards. Transfering iTunes codes can be done electronically and anonymously, and since it is something with almost world-wide demand, there is never going to be a shortage of persons willing to buy the discounted codes without asking questions.
Source: https://threatpost.com/itunes-gift-card-hack-could-be-work-carders-031609/72432/