What is DFU mode?

[danmc00]

I sold my old 3G Iphone on eBay a couple of weeks ago. The buyer has sent me a message saying this:
"hiiii i have prchase from you IPHONE 3G 8GB and just yesterday i receaved it from DHL but i realise when i switch on it appear on DFU mode....
can i know the resons and why u didnt put the softwere??"


Before I sent the phone I erased all my content off the phone. When you turn the phone on, it is asking for the connect to iTunes.


My question is, what is DFU mode?

 

[PsstGreek]

What is iPhone DFU mode?
DFU mode is a state that you can put your iPhone into where it can interface with iTunes but does not load the iPhone operating system or boot loader (this is what really differs DFU mode from recovery mode). DFU stands for Device Firmware Update.

*Taken from osxdaily.com

If your iPhone was jailbroken before you hit reset all settings, generally that is what happens. The best option to get your data off would of been a fresh restore.

Just tell the buyer he/she has to connect to iTunes and restore. It would be good as new.