Creating this alias prevents the user from overwriting this for certain
hosts in his ~/.ssh/config file.
You should add something like the folloging to you ~/.ssh/config file
to make ssh more secure by default:
# Trusted test network with changing hosts
Host *.example.net
StrictHostKeyChecking no
UserKnownHostsFile /dev/null
# Be more secure by default!
Host *
CheckHostIP yes
StrictHostKeyChecking yes
(( $+commands[ssh] )) || return
# Enforce "strict host key checking"
-alias ssh="\ssh -o 'StrictHostKeyChecking yes'"
+#alias ssh="\ssh -o 'StrictHostKeyChecking yes'"
alias sshnew="\ssh -o 'StrictHostKeyChecking no'"
alias sshtmp="\ssh -o 'StrictHostKeyChecking no' -o 'UserKnownHostsFile /dev/null'"