Firewalls can protect the gateways, carry out defined security policies, segregate the activity between the secure network, the Internet and your DMZ (the protected UTM FIREWALL zone midway between your network and the Internet, where you have the web or email server), hide internal network addresses NAT), and report threats and activity. The most threatening thing and most powerful is the combination of viruses, Trojan horses, worms, spyware/adware, phishing and pharming, which are activated with a simple click on an e-mail attachment or link.