Operation
A macro virus can be spread through e-mail attachments, discs, networks, modems, and the Internet and is notoriously difficult to detect. Uninfected documents contain normal macros. Most malicious macros start automatically when a document is opened or closed. A common way for a macro virus to infect a computer is by replacing normal macros with the virus. The macro virus replaces the regular commands with the same name and runs when the command is selected. In the cases where the macro is run automatically, the macro is opened without the user knowing.
Once the application opens a file that contains a macro virus, the virus can infect the system. When triggered, it will begin to embed itself in other documents and templates, as well as future ones created. It may corrupt other parts of the system as well, depending on what resources a macro in this application can get access to. As the infected documents are shared with other users and systems, the virus will spread. The macro virus has also been known to be used as a way of installing software on a system without the users consent as it can be used to look up software and web pages on the internet, go through with downloading and installing the software through the use of automated key-presses etc., however this is uncommon as it is usually un-fruitful for the virus coder since the installed software is usually noticed and uninstalled by the user.
A well-known example of a macro virus is the Melissa Virus from 1999. Anyone who opened a document with the virus in Microsoft Office would 'catch' the virus. The virus would then send itself by email to the first 50 people in the person’s address book. This made the virus replicate at a fast rate.
Since a macro virus depends on the application rather than the operating system, it can infect a computer running any operating system to which the targeted application has been ported. In particular, since Microsoft Word is available on Macintosh computers, word macro viruses can attack these as well as Windows platforms.
The macro virus can be avoided by exercising caution when opening email attachments and other documents. Not all macro viruses can be detected by antivirus software.
Read more about this topic: Macro Virus (computing)
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