The device failsafe utility (or Device firmware upgrade as someone says), better known as DFU
it’s a failsafe basic (and quite trivial) bootloader present on the iPhone.
This is the weak point of the iPhone 2G and hopefully 3G. This post maybe means nothing to you,
but before anyone will say I copied/robbed anything just remember you read it here first.

I will not release anything tomorrow. And I strongly suggest not to upgrade itunes nor the iPhone.

http://www.ziphone.org/2008/07/device-failsafe-utility.html