A computer virus is malware that replicates by inserting its code into other programs or files. When an infected file runs, the virus may modify additional files on the same system and, in some cases, reach other systems through shared storage, removable media, or network access. The term is often used broadly in news, but technically it describes self-replicating, host-dependent malware rather than malware in general.
Viruses matter because infection can alter legitimate software, corrupt data, or provide a foothold for further malicious activity. Security teams should treat unexpected file changes, repeated detections, and unexplained program behavior as indicators for investigation. Useful controls include regularly patched systems, endpoint protection that detects suspicious file modification and execution, restricted use of removable media, and application controls that limit unapproved code. During an incident, isolate affected hosts, preserve samples and relevant logs, identify the original execution path, and restore only from verified clean sources.