Not long after the Mac App Store opened, several warnings via Twitter began to surface. "You did implement receipt checking so that people can't pirate your app. Yes?" developer Nik Fletcher (also one of our former writers here at TUAW) asked his followers. Ged Maheux at the Iconfactory also pointed out that he was able to run a for-pay app purchased by another person, and run it on 10.5 and 10.6.5 Macs as well -- none of which should be happening, it would seem.
Receipt checking is the process that lets developers verify that the app is installed as a valid purchase by checking the embedded purchase receipt, which is included (in encry
