A file-infector is malware that embeds itself into executable files or other runnable code so the infected program carries the malicious code forward. When the host file is launched, the malware runs too, often before the user notices anything unusual. Some file-infectors also modify many files on a system, which can make cleanup harder than removing a single process or deleting one malicious file.
File-infectors matter because they can spread through normal software use, removable media, shared folders, or weakly protected applications. In real attacks, they may preserve access, drop additional payloads, or help a botnet survive by reinfecting systems as programs are opened. Defenders look for altered file hashes, unexpected changes to executables, suspicious persistence, and unusual network traffic from programs that should be clean. File integrity monitoring, endpoint detection, and controlled software execution are common defenses. In botnet cases, a file-infector may be paired with peer-to-peer communication so the malware can spread locally while still receiving updates from infected peers.