freebsd-ports/net/netsed/pkg-descr

NetSED is small and handful utility designed to alter the contents of
packets forwarded thru your network in real time. It is really useful
for network hackers in following applications:

  * black-box protocol auditing - whenever there are two or more
    propertiary boxes communicating over undocumented protocol (by enforcing
    changes in ongoing transmissions, you will be able to test if tested
    application is secure),

  * fuzz-alike experiments, integrity tests - whenever you want to test
    stability of the application and see how it ensures data integrity,

  * other common applications - fooling other people, content filtering,
    etc etc - choose whatever you want to.