Last week, we reported that Russian iOS developer ZonD8o had found a hack to circumvent paying for iOS apps. The process involved installing some security certificates and changing DNS records.
For now, there's no real "fix" that Apple can implement for iOS 5.1. However, Apple's taken steps to prevent the issue, such as blocking some of the IP addresses of the servers used by ZonD8o. The company also urges developers to validate app purchases via their own servers instead of Apple's.
It looks like developers who don't have their own servers and are still experiencing the issue are just going to have to wait it out. Apple's promised a fix for the issue in iOS 6. In the meantime, we can only hope that Apple finds a better band-aid solution.