In 1984, Dr. Frederick Cohen introduced the term “computer viruses” in his research paper titled “Computer Viruses – Theory and Experiments.” Before that, there was no name for bad coded that infected your computer.
And, just as human viruses, computer viruses are self-replicating programs that spread from one host to another. Computer viruses are classified based on the object they infect:
File infectors: There are direct and memory-resistant viruses. Direct infectors immediately infect files as soon as they are executed. What do they do?
- They overwrite host files with their own malware code resulting in the total destruction of the host file.
- As companion viruses they become extensions the host file and then create a copy of itself with the name of the host file. The renamed host file uses a hidden attribute so it does not show up in the computers directory listings.
- Or they attach themselves to the host file during infection (parasitic viruses)
Memory-Resident Viruses: These viruses do not infect files directly upon execution, but hide in the memory until a host program is executed and then infect it.
Boot-Sector Viruses: True to their name, this group of viruses infects the boot sector of a disk to get control of the computer system's execution flow even before the operating system. It basically hijacks the first instruction in the boot sector to point to itself.