A virus is a program loaded onto your computer without your knowledge that runs
against your wishes. Viruses attach themselves to programs and files in order to
spread from one computer to another. Viruses can be designed to replicate
themselves. Even a simple virus that only has the ability to replicate itself is
dangerous because it can quickly use up the computer's memory, causing the
computer to stop functioning. To spread, viruses typically require human
interaction such as forwarding an infected email or executing the virus program.
A worm is a special type of virus that has the ability to travel across the network without human interaction. Worms can attack the address book of the infected computer and send themselves to the list of email addresses. Since worms can spread through networks and replicate themselves, they quickly consume all computer memory and network bandwidth causing web servers, network servers, and individual computers to stop responding.
A trojan is a destructive program disguised as a useful one, such as a virus that appears to be an anti-virus program. Some trojans are designed to be annoying and will do such things as change your homepage or make the mouse icon disappear; however, other trojans can be quite harmful. They have the ability to open ports (internet connections) on your computer allowing access to intruders.
Often, the anti-virus software on your computer will notify you if it detects a virus or suspicious file and will give you the option to delete or clean it. As different viruses have different affects on your computer, the keen user is often the next best method of detection. Become suspicious if your computer starts functioning in an unusual or atypical manner.
To protect yourself against computer viruses, you should:
