Utility software (firewalls and anti-virus)

Anti-virus software protects your computer from viruses. How does it do this?

What does anti-virus software do if it finds a virus?

How can you make sure that you use anti-virus software properly?

What does a firewall actually do?

What is the danger of not having a firewall set up on your computer?

When do we normally have to unblock programs on a firewall?

How can you make sure that you are using your firewall safely?