Viri - Trojans -Worms
A computer virus is a computer program that can copy itself and
infect a computer without permission or knowledge of the user. A virus can only
spread from one computer to another when its host is taken to the uninfected computer,
for instance by a user sending it over a network or carrying it on a removable medium
such as a CD, DVD, or USB drive. Additionally, viruses can spread to other computers
by infecting files on a network file system or a file system that is accessed by
another computer.
Broadcast
attacks are a
thing of the past, targeted attacks are here. A Trojan
horse is a program that unlike a virus contains or installs a malicious program
(sometimes called the payload or 'trojan'). The term is derived from the classical
myth of the Trojan Horse. Trojan horses may appear to be useful or interesting programs
(or at the very least harmless) to an unsuspecting user, but are actually harmful
when executed.
A computer worm is a self-replicating computer program. It uses
a network to send copies of itself to other nodes (computer terminals on the network)
and it may do so without any user intervention. Unlike a virus, it does not need
to attach itself to an existing program. Worms always harm the network (if only
by consuming bandwidth), whereas viruses always infect or corrupt files on a targeted
computer.
What can be done?
Running an up to date OS, anti-virus with the latest definitions along
with a firewall is the first line of defense. User education and good computer usage
is the second line of defense.
What about removal?
Removing these nasties from an already infected, compromised system should be left
to professionals. You can't realize the extent of the damage with the current off
the shelf consumer products. The correct tools, skill and knowledge are nessacary
to successfully recover a compromised system and mitigate any damage that's already
been done.