Ettercap is a multipurpose sniffer/interceptor/logger for switched
LAN.  It supports active and passive dissection of many protocols
(even ciphered ones) and includes many feature for network and host
analysis. 

It's possible to sniff in four modes.

+ IP Based, the packets are filtered on IP source and destination
+ MAC Based, packets filtered on mac address, useful to sniff
  connections through gateway
+ ARP based, uses arp poisoning to sniff in switched lan between
  two hosts (full-duplex).
+ PublicARP based, uses arp poisoning to sniff in switched LAN
  from a victim host to all other hosts (half-duplex). 
          
Cool Features:

Characters injection in an established connection :
  you can inject character to server (emulating commands) or to
  client (emulating replies) maintaining the connection alive !!

SSH1 support:
  you can sniff User and Pass, and even the data of an SSH1
  connection. ettercap is the first software capable to sniff an
  SSH connection in FULL-DUPLEX

Plug-ins support:
  You can create your own plugin using the ettercap's API.

Password collector for:
  TELNET, FTP, POP, RLOGIN, SSH1, ICQ, SMB, MySQL, HTTP
  (other protocols coming soon...) 

OS fingerprint:
  you can fingerprint the OS of the victim host and even its
  network adapter 

Kill a connection:
  from the connections list you can kill all the connections you want 

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