By now, you may have heard numerous warnings about not opening email attachments unless you fully trust the sender and are expecting the attachment. Opening attachments from unknown sources is the most common way you can become infected with and spread malicious software known as worms.
But how do computer worms actually spread? Understanding the answer to this question will help you learn the steps you can take to protect yourself and others.
A virus is a computer program that seeks to spread from one computer to another by attaching itself to a computer file. A virus typically requires human action, such as sharing a file or opening an email, to propagate. A computer worm, like a virus, is designed to replicate itself from one computer to another, but it does so automatically by taking control of features within the computer that can transmit files or information. Once a worm is in your system, it can move on its own. A significant danger of worms is their ability to reproduce in large quantities.
How Your Computer Can Become Infected
Hackers have become experts at disguising computer worms as email attachments. When an unsuspecting user opens the attachment, the worm is activated and, depending on the hacker’s intent, will automatically send itself as an email attachment to everyone in that user’s address book.
The Mydoom worm, which began appearing in February 2004, used particularly sophisticated techniques to convince users to click on the attached file. Its creator carefully crafted several error messages that looked legitimate, using various headers such as “Mail Delivery System,” “Test,” or “Mail Transaction Failed.” You may often receive these types of emails. They are formal messages informing us that one of the emails sent did not reach its recipient. They often contain technical language that most of us do not understand. The creator of Mydoom mimicked this language in a way that could deceive millions into opening the attachment.
Subsequent versions of Mydoom employed frightening techniques, including sending emails that appeared to be from Internet Service Providers (ISPs) warning you that you were infected with a worm and that the only way to eliminate it was to open the attachment. As you might guess, those attachments contained the worm.
How Worms Spread from One Computer to Many
One of the sophisticated reproductive techniques of a worm is sending out numerous emails with dangerous attachments to everyone in the user’s address book. In this way, it disguises itself as an email from a trusted friend. Therefore, it is extremely important to be cautious before opening an email attachment.
Attacks
In addition to self-replication, worms can program themselves to perform other activities. For example, Mydoom was designed so that infected computers (also known as “zombie computers”) would launch attacks on specific targets at a specific time. These attacks, known as Distributed Denial of Service (DDoS) attacks, are designed to overwhelm their targets with traffic and cause them to crash.
Prevention and Elimination
The best way to prevent worm infections is to be cautious when opening email attachments. If you receive an attachment in an email from a friend, the safest course of action is to contact them and ask if they intended to send the attachment. If you receive an attachment from someone you do not know, the safest option is to delete it.
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