Which virus type is known for executing when a user opens a document?

The virus type that is known for executing when a user opens a document is the Document Virus. Document viruses are designed to be embedded within documents, often in formats such as Microsoft Word or Excel. These viruses usually exploit the features of document editing software to execute malicious code when the document is opened or a particular action is taken by the user, like enabling macros.

Users are often tricked into opening infected documents, thinking they are safe. Once the document is opened and any necessary permissions are given, the virus can execute and potentially infect the user's system. This method of delivery is particularly insidious because it relies on social engineering, prompting users to engage with the virus, often without their knowledge.

In contrast, other virus types, like boot sector viruses, typically execute when a computer boots from an infected disk, rather than through document interaction. Overwriting viruses can damage files by replacing their content but aren't specifically tied to the opening of a document. Companion viruses, while they can exploit a process related to executing files, don’t specifically target documents in the manner that Document Viruses do.