How does web based jailbreak work for iPhone?

I hope everyone knows that there is this web based jailbreak at jailbreakme.com

I was initially skeptic but it worked on my iPod touch.

Can someone explain how it works ? How can a website jailbreak my hardware ? Is it like some virus which affects our computer when we visit certain websites ? How can it开发者_C百科 execute a program on my iPod touch ? What kind of program is it ?

If that was the case, why didn't anyone release a small web server which can be run on our PC/Macbook to jailbreak our iPhone/iPod touch by just visiting localhost on its web browser ???

The website says that the jailbreak is reversible but doesn't it void the Apple's warranty ??? Does it cause any permanent damage ?

I want to try it on my iPhone4 but hesitant if it would void my warranty ...

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The jailbreakme.com utilizes a vulnerability in the iPhone (and OSX's) PDF font rendering to allow it to execute arbitrary code. Thus installing Cydia.

I've done it today on my 3GS and it's worked awesomely.

It is reversable by a software restore in iTunes.