.
A review of the development of personal computers and multi-tasking workstations will show that the gap in functionality between these classes of systems is narrowing rapidly. In the future, a single system may meet all of the requirements necessary to support both worms and viruses. This implies that worms and viruses may begin to appear in new classes of systems. A knowledge of the histories of viruses and worms may make it possible to predict how malicious code will cause problems in the future. .
Basic Definitions.
To provide a basis for further discussion, the following definitions will be used throughout the report;.
Trojan Horse - a program which performs a useful function, but also performs an unexpected action as well; .
Virus - a code segment which replicates by attaching copies to existing executables; .
Worm - a program which replicates itself and causes execution of the new copy and .
Network Worm - a worm which copies itself to another system by using common network facilities, and causes execution of the copy on that system. .
In essence, a computer program which has been infected by a virus has been converted into a "trojan horse". The program is expected to perform a useful function, but has the unintended side effect of viral code execution. In addition to performing the unintended task, the virus also performs the function of replication. Upon execution, the virus attempts to replicate and "attach" itself to another program. It is the unexpected and uncontrollable replication that makes viruses so dangerous. As a result, the host or victim computer falls prey to an unlimited amount of damage by the virus, before anyone realizes what has happened.
Viruses are currently designed to attack single platforms. A platform is defined as the combination of hardware and the most prevalent operating system for that hardware. As an example, a virus can be referred to as an IBM-PC virus, referring to the hardware, or a DOS virus, referring to the operating system.
