Russian developer ZonD8o's found a way to circumvent paying for apps in the App Store with devices running iOS 3.0 to 6.0. His method also doesn't even require a jailbreak.
ZonD8o put up a video detailing a relatively simple way to circumvent for paying for apps, although it's now been taken down at Apple's request. The steps in the video include installing some security certificates, including one from ZonD8o's own site In-AppStore.com (a site dedicated to Apple hacks), and changing DNS records in Wi-Fi settings.
After taking these steps, users, instead of receiving the usual purchase confirmation box, will receive a dialogue box that says "If you like in-appstore.com, click the button!" The app will then be "purchased" and ready for install.
9to5Mac tried to hack and has confirmed that it worked. However, Apple's been made aware of the issue and is actively investigating it. This is the comment that Apple's put out regarding the hack: "The security of the App Store is incredibly important to us and the developer community. We take reports of fraudulent activity very seriously and we are investigating."
Hopefully, this security issue gets patched soon. Otherwise, free apps for all.