RE: ideal OS distro for network scanning?

Best os depends on the one you know best.
If you can't configure it, or don't know how to optimize it, the best
os, mis-configured will be the worst os.

> I like OpenBSD's security paranoia (don't want the scanner 
> being compromised), but I also understand that linux can be 
> hardened as well, so my second concern is the underlying OS 
> skewing the results of a network scan and the ability for the 
> OS to stay out of the way of the scan results.

Biggest issues with scans would be the firewall used (if any)
If you feel comfortable deploying 'your os' without any firewall, do
that.

If you do this, and use a dual homed system, make sure you bind internal
things like nessusd to localhost, and remote access like ssh to the
internal nic.

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