What is a Macro Virus? - Definition

A macro virus is a computer virus that alters or replaces a macro, which is a set of commands used by programs to perform common actions. For example, the "open document" action in many word-processing programs relies on a macro to function, since there are several discrete steps in the process. Macro viruses change this command set, allowing them to execute whenever the macro is run.

Sources of Macro Viruses

Macro viruses are most commonly found embedded in documents or inserted as malicious code into word-processing programs. They may come from documents attached to emails, or the code may be downloaded after clicking on "phishing" links in banner ads or URLs. They are difficult to detect, as they do not operate until an infected macro is run, at which time they perform a series of commands. A macro virus is similar to a Trojan virus, since it may appear benign and users may not immediately notice any ill effects. Unlike Trojans, however, macro viruses can replicate themselves and infect other computers.

Risk Factors

The main risk of macro viruses is their ability to spread quickly. Once an infected macro is run, all other documents on a user's computer become infected. Some of these viruses cause abnormalities in text documents, such as missing or inserted words, while others access email accounts and send out copies of infected files to all of a user's contacts, who in turn open and access these files because they come from a trusted source.

These viruses can also be designed to erase or compromise stored data. In addition, it's important to note that macro viruses are cross-platform; they can infect both Windows and Mac computers using the same code. Any program that uses macros can operate as a host, and any copy of an infected program — sent via email, stored on disk or on a USB drive — will contain the virus.

To remove these viruses, users should rely on security software that provides specific macro virus detection and removal tools. Regular scans will clean any infected documents and ensure no new computer viruses are downloaded.

Types of Macro Viruses

  • Concept Virus
    Concept was the first macro virus, appearing in July 1995 and targeted Microsoft Word. Macro viruses subsequently became the dominant type of virus.

  • Melissa Virus
    Melissa made history as the first macro virus with email worm trait and started spreading via email on March 26, 1999 infecting tens of thousands within hours. It was one of the most serious epidemics in Internet history.

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