以下是使用 nmap 探测目标主机的操作系统的两个实例（两种方法都没有探测到）。nmap 工具可以上 http://insecure.org/nmap 网站下载。

一、

D:\Program Files\nmap-5.21>nmap -A 192.168.1.20 | more

Starting Nmap 5.21 ( http://nmap.org ) at 2010-01-30 22:31 中国标准时间
Nmap scan report for 192.168.1.20
Host is up (0.00s latency).
All 1000 scanned ports on 192.168.1.20 are filtered
MAC Address: 00:1D:72:2E:F7:64 (Wistron)
Too many fingerprints match this host to give specific OS details
Network Distance: 1 hop

HOP RTT     ADDRESS
1   0.00 ms 192.168.1.20

OS and Service detection performed. Please report any incorrect results at http:
//nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 30.05 seconds

二、

D:\Program Files\nmap-5.21>nmap -O 192.168.1.20 | more

Starting Nmap 5.21 ( http://nmap.org ) at 2010-01-30 22:34 中国标准时间
Nmap scan report for 192.168.1.20
Host is up (0.00s latency).
All 1000 scanned ports on 192.168.1.20 are filtered
MAC Address: 00:1D:72:2E:F7:64 (Wistron)
Too many fingerprints match this host to give specific OS details
Network Distance: 1 hop

OS detection performed. Please report any incorrect results at http://nmap.org/s
ubmit/ .
Nmap done: 1 IP address (1 host up) scanned in 27.27 seconds