Most viruses encountered in microcomputers are acts of vandalism. Usually, a virus begins as a practical joke or an experiment. Bootstrap virus codes replace the bootstrap code in memory. COM file in DOS-based computers. Joiner viruses act by joining with the system files necessary for the operation of the computer.
Attachments are viruses that attach themselves to a utility or an application program.
Another way to consider viruses is how they affect the system. There are five methods of attack. This type is often called a time bomb or logic bomb. Bombs are programs that remain dormant until activated by a date, time, use, function, or the number of times a particular function is performed. When this event occurs, the program is activated.