Apple has released a security fix for iOS 4 and users now have to decide whether or not to install the update. There are pros and cons to installing the update, mostly revolving around whether or not you're interested in jailbreaking your device. The security problem was first discovered and used by the Dev-Team to hack iOS 4 and provide a simple way to jailbreak through the Safari browser.
Now that Apple has released a fix, the developer responsible for the JailbreakMe 2.0 in-browser jailbreak software has made the source code of his exploit public. Let's be clear, the iOS 4.0.2 update will make jailbreaking with JailbreakMe 2.0 impossible, however now that the source code of the jailbreak is public, security threats are bound to multiply.