Amazon Android DevicesAmazon has advised Android developers that if they're worried about reverse engineering of their apps, they should consider obfuscating their code. Once developers download their software development kit, a tool called ProGuard can make the source and machine code difficult for humans to decipher. The program shrinks, optimizes and obscures the source code while reducing file sizes and increasing run-time performance, Amazon says. However, it warned that code can't be obfuscated in applications allow in-app purchasing, such as in-game currency, digital content and subscriptions. Amazon wants to be able to contact developers using its Appstore should there be issues with purchase requests, but it can't do that if the contact information is obfuscated. Amazon also announced that it's established new parental controls allowing it to drop its $20 limit for in-app purchases. Last year, Apple ran into problems when children with iPods, iPhones or iPads ran up megabuck tabs on their parents' bills. Amazon's one-click purchasing makes this even easier. But now in-app purchases will require an Amazon password or a four-digit PIN. According to research by CCS Insight and Distimo, in-app purchases make up 60 percent of revenue among the 200 highest-grossing applications for Apple and Android. And mobile analytics company Flurry found that transactions of more than $20 make up the bulk of that revenue.