The term, virus, in computer technology, refers to a self replicating application that spreads by making copies of itself by inserting into other programs, other executables or documents, and when executed begins to perform harmful actions on the system. All computer viruses are deliberately created, not always malicious and some of them may be benign and simply annoying.
Non-Memory Resident and Memory Resident Viruses:
Non-Memory resident viruses, when they are executed, immediately look for other hosts that can be infected. When they infect these targets, they transfer control to the application program they infected. A non-resident virus has a finder module and a replication module. The finder module, once it finds a new file to infect, calls upon the replication module to infect that file.
Memory-Resident virus stays in the memory and do not look for hosts to infect when they are executed. It stays active in the background after its host program is terminated, and infects files as soon as they are opened or accessed by other programs or the operating system. It does have the replication module like the non-memory resident virus, but without the finder...