If you are using ports the update requires some manual intervention.
The following procedure should be followed:

# pkg query %ro libiconv >ports_to_update
# pkg delete -f libiconv
# cat ports_to_update | xargs portmaster

or:

# pkg query %ro libiconv >ports_to_update
# pkg delete -f libiconv
# cat ports_to_update | xargs portupgrade -f

その他にも色々罠は待ち構えている