firewall
... The solution was the firewall. A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. The firewall acts as a gatekeeper and monitors all the information traveling to and from a network. ... A firewall is typically a computer that is placed between the Internet and the network you want to protect. ... All data between the Internet and the protected network must go through the firewall. The firewall provides several services based on important information found in this data; such as an access control, authentication, activity logging, and alarm warnings. The key to all these services are lies in the networking information contained in each piece of chunk of data passing through the firewall. ... A packet filtering firewall is the simplest type of firewall. ... For example, firewall will sniff each packet of information for an exact match of the text listed in the filter. You could instruct the firewall to block any packet with the word “X-rated” in it. ... The second is proxy service that information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa. ... Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. ... A further brand of firewall that is good is ZoneAlarm.