Malware
Resident Virus
Also known as: Memory-resident virus
Definition
A virus that installs itself in memory so it can run continuously and infect files or processes long after its host program has exited.
Examples
- Randex and CMJ, classic memory-resident DOS viruses.
- Magistr and Funlove that hooked Windows APIs to infect executables on access.
Related terms
Computer Virus
Malicious code that inserts copies of itself into other programs or files and executes when the host is run.
Non-Resident Virus
A virus that does not stay in memory after execution; it searches for and infects target files only while the host program runs, then exits.
Stealth Malware
Malware specifically engineered to evade detection by users, security tools, and forensic investigators through hiding, mimicry, and anti-analysis tricks.
Polymorphic Malware
Malware that changes its on-disk appearance — typically via re-encryption or packing — for each infection, while keeping its core logic intact.
Fileless Malware
Malware that runs primarily in memory and leverages trusted system tools, avoiding the use of traditional executable files on disk.
Rootkit
Stealth malware that grants and hides privileged access to an operating system or device, evading detection by standard tools.