10 Worst Computer Viruses of All Time : Melisaa

Computer viruses can be a nightmare. Some can wipe out the information on a hard drive, tie up traffic on a computer network for hours, turn an innocent machine into a zombie and replicate and send themselves to other computers. If you've never had a machine fall victim to a computer virus, you may wonder what the fuss is about. But the concern is understandable -- according to Consumer Reports, computer viruses helped contribute to $8.5 billion in consumer losses in 2008. Computer viruses are just one kind of online threat, but they're arguably the best known of the bunch.

Computer viruses have been around for many years. In fact, in 1949, a scientist named John von Neumann theorized that a self-replicated program was possible. The computer industry wasn't even a decade old, and already someone had figured out how to throw a monkey wrench into the figurative gears. But it took a few decades before programmers known as hackers began to build computer viruses.

While some pranksters created virus-like programs for large computer systems, it was really the introduction of the personal computer that brought computer viruses to the public's attention. A doctoral student named Fred Cohen was the first to describe self-replicating programs designed to modify computers as viruses. The name has stuck ever since.

We're going to take a look at 10 of the worst computer viruses to cripple a computer system. Let's start with the Melissa virus.

1) Melissa

In the spring of 1999, a man named David L. Smith created a computer virus based on a Microsoft Word macro. He built the virus so that it could spread through e-mail messages. Smith named the virus "Melissa," saying that he named it after an exotic dancer from Florida.

The Melissa computer virus tempts recipients into opening a document with an e-mail message like "Here is that document you asked for, don't show it to anybody else." Once activated, the virus replicates itself and sends itself out to the top 50 people in the recipient's e-mail address book.

The virus spread rapidly after Smith unleashed it on the world. The United States federal government became very interested in Smith's work -- according to statements made by FBI officials to Congress, the Melissa virus "wreaked havoc on government and private sector networks". The increase in e-mail traffic forced some companies to discontinue e-mail programs until the virus was contained.

After a lengthy trial process, Smith lost his case and received a 20-month jail sentence. The court also fined Smith $5,000 and forbade him from accessing computer networks without court authorization [source: BBC]. Ultimately, the Melissa virus didn't cripple the Internet, but it was one of the first computer viruses to get the public's attention.

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