When the genius minds of the iPhone hacking community discovered that just about every iPhone around was vulnerable to a PDF rendering bug that allowed for one-click jailbreaking, the geek world celebrated — until someone pointed out that this was really, really scary. Deep running system controls, accessible via a browser exploit? As our Spanish-speaking friends around the world would say: No bueno.

Fortunately, Apple didn’t just kick back and hope nothing bad would happen.

Even with iOS 4.1 in the beta stages of its development, Apple has just released an emergency update: iOS 4.0.2. The purpose of the update appears to be solely focused on patching out the PDF exploit.

The good news? No crazy hackers stealin your databytes after you accidentally click on a seemingly harmless PDF. The bad news? One-click, browser-based jailbreaking (the only kind that has been made public so far for the iPhone 4 and any device running iOS 4) is a done deal for now. If your iPhone-happiness depends on contraband items like like Cydia and Grooveshark, it’s best to stay away for now — but be careful what you click.