Pentoo Linux for Penetration Testing - Review and Commentary - Linux Critic
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We don't do much network pentesting, but Backtrack is still really handy to have around, especially for anything involving wireless, since the driver stack is all set up on it.
I tend to find Backtrack provides a decent starting point, but most of the testers (and all of the full time day-in-day-out testers) I know tend to use their own Linux systems on live network tests. We use VMWare images for both Windows and Linux, which lets us work in situations where clients don't want our laptops plugged in, or where the data can't leave site.