I\'ve just released an app, a paid app, 4 days later a user told me there\'s another web site in China hosts my app. I downloaded it from there, and it does run fine on my d
The best thing to do is not worry about it. The people pirating it in China are not your customers, and never will be. If there was no pirate version available they still wouldn't pay you for a copy, in all probability. Besides which if your app becomes popular it will be cloned anyway, just like iOS apps are. The security systems you have already implemented are all that you need as they prevent most users from pirating the app.
Trying to make your app piracy proof will just harm the code base and make it harder to maintain, as well as potentially introducing problems for your genuine paying customers. Instead focus on promoting your app and making it easy for customers to pay for and use. By being responsive to feature requests and bug reports you add value that people are willing to pay for, rather than seeking out some dodgy cracked copy from a Chinese web site that is probably a trojan anyway.
Finally, report the pirate copies to anti-virus vendors. Supply copies of the APK. They will add signatures to their databases so that it gets flagged up as potentially dangerous.