Winpwn 2.0.0.3

[Gmane]

Ok this might be a dumb question but i'm trying to use winpwn and i just want to know where do i find the ipsw file? is this a file that has to be downloaded or can i use an existing file from my PC? does itunes create a ipsw to do a restore if so where do i find it so i can create my custom ipsw?

Thanks