Final answer:
The default policy for maximum security in iptables is to DROP all packets that do not match an explicit rule, providing no response to the sender and thus increasing security.
Step-by-step explanation:
The default policy for packets in iptables for maximum security is to DROP them. This setting means that any traffic that does not explicitly match a rule in the iptables rule set will be silently dropped, i.e., ignored without sending any response to the sender. This is often done to protect a system from potentially harmful traffic by not engaging in any form of communication with unknown or untrusted sources. The DROP policy goes further than REJECT, which would inform the sender that the packet was not accepted, potentially revealing the existence of a server to a would-be attacker.