in reply to
Remote OS Detection
I would use nmap to do that.
This may not be the best approach, since they have legitimate access to the systems in question. See A practical approach for defeating Nmap OS-Fingerprinting.
IIRC there are other more subtly ways of achieving this sort of thing.
Also nmap may not be an option. Yesterday pankaj_it09 asked if it was possible to use Nmap::Parser without having nmap installed on the host system.
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