Firewalls Series#1
Stateless-Firewalls/Packet-Filtering:
Remember that these types of firewalls don't check the inside of these packet for malware, so if the protocol number, source and destination IP and port match the rules (ACL) you've set up, the packet will enter your LAN and infect your computer. Its best to combine these types of firewalls with other types, such as a Proxy Server (Application-Level Gateway)
More on Packet-Filtering here
https://cyber-defense.sans.org/resources/papers/gsec/packet-filter-basic-network-security-tool-100197
