a security threat is a potential cause of unwanted
incident, which may result in harm to a system
security threats are like Errors and Omissions, Fraud
and Theft, Employee Sabotage, Loss of Physical and
Infrastructure Support, Malicious Hackers, Industrial
Espionage, Threats to Personal Privacy.
Virus: A code segment that replicates by attaching copies
of itself to existing executables. The new copy of the virus
is executed when a user executes the new host program.
The virus may include an additional "payload" that triggers
when specific conditions are met. For example, some
viruses display a text string on a particular date. There are
many types of viruses, including variants, overwriting,
resident, stealth, and polymorphic.
Trojan Horse: A program that performs
a desired task, but that also includes
unexpected (and undesirable) functions.
Consider as an example an editing
program for a multiuser system. This
program could be modified to randomly
delete one of the users' files each time
they perform a useful function (editing),
but the deletions are unexpected and
definitely undesired!
Worm: A self-replicating program that is
self-contained and does not require a host program.
The program creates a copy of itself and causes it to
execute; no user intervention is required. Worms
commonly use network services to propagate to
other host systems.