Which virus type is triggered when a document containing it is opened?

The correct answer is a Macro Virus. This type of virus is designed to attach itself to documents that use macros, such as word processing or spreadsheet files. When the infected document is opened and the macros are executed—often automatically or with the user’s permission—the macro virus is triggered. This allows it to spread or perform malicious actions, such as corrupting files, stealing data, or transmitting itself to other documents.

Macro viruses leverage the functionality of macro programming languages embedded in applications like Microsoft Word or Excel, making them particularly effective in infecting systems through benign-looking documents. This is why it is essential to enable macro settings cautiously and be wary of opening documents from untrusted sources.

The other types of viruses mentioned do not respond to the opening of documents in the same way. A Boot Sector Virus infects the master boot record of a storage device and activates when the computer starts up, not upon opening a document. A Multipartite Virus can spread in multiple ways but typically does not rely solely on document opening to activate. Metamorphic Viruses change their code each time they infect a system, making them harder to detect, but they are also not specifically activated by opening a document.