In what may be the ultimate in "Far East knockoffs," some enterprising hackers in China have reverse-engineered the iTunes Gift Certificate algorithm — and are now selling working knock-off cards for pennies on the dollar. For example, inside China itself, US$3.00 will get you a US$200.00 certificate that, as far as iTunes is concerned, walks, talks, and purchases just like the real thing. These "working fakes" have even made it to the West, where a recent eBay listing offered the same two-Benjamin counterfeit for US$40.00.
The problem here (aside from the, y'know, complete illegality of it) is twofold. First, it's statistically possible that the Chinese technique could generate a card code that already exists legitimately, thereby screwing the rightful owner out of their card's value. Secondly, the House of Jobs (who have remained mum so far on the issue) could re-jigger the code-generating process, but once again leave a lot of valid customers SOL.