Circuit-level gateways monitor TCP handshakes and other network protocol session initiation messages across the network as they are established between the local and remote hosts to ascertain whether the session being initiated is legitimate or whether the remote system is regarded as trusted. This is another relatively quick method of identifying malicious content. However, they don’t check the packets themselves. Although packet filtering firewalls are less secure than circuit-level gateways, they should still use them in conjunction with other systems. For instance, application-level gates are frequently used in conjunction with circuit-level gateways. This approach combines content filtering with the benefits of packet- and circuit-level gateway firewalls.