A/D

https://www.quora.com/anonymous/2071f6ebe15c40e7ae70001a0420222a

--String

You'd need a kernel compiled with Netfilter "String match support" enabled.

iptables -A INPUT -m string --algo bm --string "test" -j DROP
iptables -A OUTPUT -m string --algo bm --string "test" -j DROP
iptables -A FORWARD -m string --algo bm --string "test" -j DROP