A macro virus is a type of computer virus that is written in a macro language, which is a programming language embedded inside a software application such as Microsoft Excel or Word. Macro viruses can be spread through e-mail attachments, removable media, networks, and the Internet, and are notoriously difficult to detect. They work by adding their code to the macros associated with documents, spreadsheets, and other data files, and can infect any operating system. Once a macro virus infects an application, it executes a series of commands and a sequence of actions that begin automatically when the application is opened. These malicious macros may start automatically when a document is opened or closed, without the users knowledge. Macro viruses have been used as a method of installing software on a system without the users consent, as they can be used to download and install software from the internet through the use of automated key-presses. Some of the actions that a macro virus can perform include deleting, corrupting, or moving files, sending files, and even installing other types of malware.

To prevent macro viruses, it is recommended to use strong antivirus software that can detect these threats automatically. Users should also exercise caution when opening email attachments and other documents, and avoid enabling macros unless they are absolutely necessary.