How computer virus work

Virus Worms. Cure Virus. New Computer Viruses. Security Viruses. Symantec Viruses. How Computer Viruses Work. How Worms Work: Code Red. Virus Origins and History. Virus Evolution. How to Protect Your Computer from Viruses. Lots More Information. See all Internet articles. Computer viruses tend to grab our attention. On the one hand, viruses show us how vulnerable we are. A properly engineered virus can have an amazing effect on the worldwide Internet.

On the other hand, they show how sophisticated and interconnected human beings have become. Your Browser Does Not Support iFrames In this article, we will discuss viruses -- both "traditional" viruses and the newer e-mail viruses -- so that you can learn how they work and also understand how to protect yourself.

The most common are: Viruses - A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce by attaching to other programs or wreak havoc.

But some of the most widespread disruption comes from botnets. Malicious code, often spread through email attachments, installs itself on thousands of computers. The hijacked machines act as an unwitting army of zombies firing off spam emails or blitzing targets like defence or corporate mainframes. They overwhelm them with a barrage of requests for information in so-called distributed denial of service attacks. Finally, the virus hands control to the application as if nothing had happened.

Because of this, reinstalling a fresh copy of an infected application on a system infested with a non-resident virus makes little difference, because it can quickly become reinfected by other applications.

With the rise in popularity of Microsoft Office in the early s, virus programmers began to use another non-resident virus technique. Office documents allow you to embed macros written in Word Basic that run automatically when you open the file. If the macro is malicious, you're in trouble. This is how the Concept virus of worked. This virus is thought by some to be the most widespread virus infection of all time. Social engineering has always played a huge part in spreading viruses.

Everyone loves free stuff, and virus writers often infect pirated software in order to spread their work. Others write Word documents purporting to contain passwords for porn sites and infect them with macro viruses.

The Melissa virus of was a good example of this ploy. Its payload tried to mass-mail the infected document to the first 50 people in the infected user's Outlook Express address book. While true viruses only infect files on a single system unless users decide to swap files , Melissa could copy itself to new computers without human intervention.

Because of this, it's classed as a computer worm. The same basic technique was used to spread the famous I Love You virus of , whose malicious payload also made changes to infected systems. Current page: How viruses work.