As the spread of viruses and
malware becomes more prevalent, it is vitally important that
every PC with a connection to the Internet have at the very
least an active Anti-Virus program. Those users with DSL or High
Speed Cable access should also employ the use of a Firewall.
What
is Malware?

According to Wikipedia, malware is short for "malicious
software," and is specifically designed to damage or disrupt a
computer system.
What is a Virus?

The classic definition of a virus is "a self-replicating program
that spreads by inserting copies of itself into other executable
code or documents." The biggest effect of a virus on a computer
system is the constant reproduction that eventually overwhelms a
computer's resources.
Virus/Malware
Sources:

The major sources of viruses and malware are: pornography sites,
shareware sites, downloadable games, supposedly "helpful"
programs such as those that promise increased Internet speeds,
and emails with infected attachments.