Information Technology Reference
In-Depth Information
It is typical for viruses to either not infect or propagate further upon detection of a
previous infection. This prevents duplicate infections or even potential incompatibili-
ties in multiple infection operations. However, if the virus has determined that it is on
a “virgin” system, it infects the host and begins either replication or infection. Melissa
performs self-replication immediately upon determination of first execution.
Here, additional environmental information is obtained and if the conditions are
met, in this case determining if the e-mail client is Microsoft Outlook, self-replication
begins. The code snippet below shows the self-replication portion of Melissa.
Melissa sends e-mail with the subject “Important Message From <Username>” to
the first fifty entries in every address book that the user executing the virus has ac-
cess. In the message, the document containing the Melissa virus is attached. Unfortu-
nately for the computing community, e-mail is one of the quickest methods of trans-
mission. Unsuspecting users would receive the e-mail, open the attachment and
proceed to infect themselves.
The rate of self-replication varies depending on the mechanism of infection. If a vi-
rus infects a host from a floppy disk boot sector, the infection rate is relatively slow,
