First of all we would like to know what exactly are virus, Trojan horse and worms. Viruses, worms, and Trojans are malicious programs which enter to your computer without your permission and knowing that can cause damage, information losses, privacies leak to your computer .They can also slow down the Internet connections, and they might even use your computer to spread themselves to your friends, family, co-workers, and the rest of the internet. The good news is that with an ounce of prevention and some good common sense, you are less likely to fall victim to these threats. Think of it as locking your front door to protect your entire family for example you will never open anonymous mails or attached file and always keep you computer security up to date like latest firewall, antivirus programs and etc.
What is virus? A computer virus, according to Webster 's Collegiate Dictionary, is "a computer program usually hidden within another seemingly innocuous program that produces copies of itself and inserts them into other programs or files, and that usually performs a malicious action (such as destroying data)". Two categories of viruses, macro viruses and worms, are especially common today. Computer viruses are never naturally occurring; they are always man-made. Once created and released, however, their spread is not directly under human control. One example of a virus is the Anna Kournikova virus, which comes in the form of a picture sent through email.
What are worms? Worms are very similar to viruses in that they are computer programs that replicate functional copies of themselves (usually to other computer systems via network connections) and often, but not always, contain some functionality that will interfere with the normal use of a computer or a program. The difference is that unlike viruses, worms exist as separate entities; they do not attach themselves to other files or programs. Because of their similarity to viruses, worms are
References: 1) Worst-Case Worms Could Rack up $50 Billion in U.S. Damages Gregg Keizer, TechWeb News http://internetweek.com/security02/showArticle.jhtml?articleID=21401723 2) Cashing in on Virus Infections Michelle Delio, Wired News http://www.wired.com/news/infostructure/0,1377,62558,00.html?tw=newsletter_topstories_html 3) Let 's talk about Viruses http://www.hasd.org/virus/virus.htm 4) Computer Abuse http://ethics.csc.ncsu.edu/abuse/