PromiscDetect for Windows NT 4.0 / 2000 / XP checks if your network adapter(s) is in promiscuous mode or not (that is, in most cases, if a sniffer is running on the computer or not). Of course the attacker might be intercepting the communication between the tool and the adapter, making the result unreliable, but there are probably many more cases out there where the tool will really detect a sniffer.
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