It may be only a distraction to the operator. It is infectious, spreading by duplication. However, it may not infect these systems unless they are specific targets. It can remain dormant within the carrier until it connects with a system that can be infected. A virus might remain dormant for months before it is activated by the computer's internal clock or calendar.
Viruses can spread in several ways.
They may be spread by multiple users on one microcomputer or by copying a file from an electronic bulletin board or downloading a file from a mainframe. They may be spread by simply moving a data file from one microcomputer to another microcomputer. In college microcomputer labs, viruses are spread by the use of the computer by several users during a day. As a prank, a person may introduce a virus to a DOS disk that is used on several microcomputers during the day. Another way a virus can spread is by employees taking floppy disks home and working on them on their home computers.