A computer virus is a program that invades your computer system, hides there, and makes copies of (replicates) itself. Viruses spread when you launch an infected application or start up your computer from a disk that has infected system files.
Viruses behave in different ways. Some viruses stay active in memory until you turn off your computer. Other viruses stay active only as long as the infected applications is running. Turning off your computer or exiting the application removes the virus from memory, but does not remove the virus from the infected file or disk.
Some viruses are programmed specifically to damage the data on your computer by corrupting programs, deleting files, or erasing your entire hard disk.
All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt.
Computer viruses are frequently spread by attachments in email messages or by instant messaging messages. Therefore, you must never open an email attachment unless you know who sent the message or you are expecting the email attachment. Viruses can be disguised as attachments of funny images, greeting cards, or audio and video files. Computer viruses also spread through downloads on the Internet. They can be hidden in pirated software or in other files or programs that you might download.
Trojan horses are not viruses; however, they are often thought of as viruses. A trojan horse is a program that appears to serve some useful purpose or provide entertainment, which encourages you to run it. But, like the Trojan horse of old, it also serves a covert purpose which may be to damage files or perhaps plant a virus on your computer.
A worm is computer code that spreads without user interaction. Most worms begin as email attachments that infect a computer when they’re opened. The worm scans the infected computer for files, such as address books or temporary webpages, that contain email addresses. The worm uses the addresses to send infected email messages, and frequently mimics (or spoofs) the “From” addresses in later email messages so that those infected messages seem to be from someone you know. Worms then spread automatically through email messages, networks, or operating system vulnerabilities, frequently overwhelming those systems before the cause is known. Worms aren’t always destructive to computers, but they usually cause computer and network performance and stability problems.
Many computer viruses turn out to be hoaxes or myths. Hoaxes are false alerts about viruses that don’t exist. For a list of hoaxes check out Snopes.
We highly recommend that you have Virus Protection installed in your computer before you consider downloading anything. Here are the most popular anti-virus websites:
Provides content and network security software and appliance products to individuals, enterprises, and service providers.
Provider of software application services for PC users.
Supplier of enterprise-wide network security and management software.