[Think of the Computer as a Multi-Story Office Building]; to help explain Computer Security in Non-Technical terms. People are running errands from this Building to the rest of the town. The rest of the town is the Internet containing other buildings (Computers). Each building has doors on the ground level (Computer Ports) in which different types of people are entering and leaving.
A Firewall places a Security Person at each door (Port) to check Identification badges, the packages of each person and determine if they are allowed to enter the Intranet Zone which is the 20 Story Building. The town is the Internet Zone. With good security the doors (Ports) to the Building will be protected (Closed) and with a Top–Notch Firewall the whole building will appear to disappear (Stealth) as viewed from the town (Internet).
Criminal elements try to sneak (Inject) Malware into the building (Computer) by impersonating the people who go in and out. Or, without a properly secured Firewall they will use an unprotected door to enter. If the criminal is successful, a Malware (package) will be placed in a clever place attempting to avoid detection.
An Anti-Malware Program works within the building (Computer) to watch the activities of each person in the building and puts a special tag on them. Any person in the building without a valid tag is immediately placed under arrest (Quarantine) and with approval the police are called to take them away.
The SCAN command used by Anti–Malware Software directs its Security Team to search throughout the building to find any Malware (packages) that might have gone undetected. The Anti-Malware Program uses the Most–Wanted–List (Signature File) to identify bad people and packages. It also knows how most bad people act (Malware) and endeavors to identify new criminals who have not yet been added to the Most–Wanted–List (Heuristics).
To recap, the Firewall secures the doors and the Anti–Malware uses the latest Most–Wanted–List (Signature File) to identify the good or bad people and packages.
(Excerpt from the Computer-Appliance-Learning-Maintenance-Manual)
TECHIMPROVED (Napa Valley Security Consulting) 