What is Malicious Code?

What is Malicious Code?
Malicious code is any code added, changed, or removed from a software system in order to intentionally cause harm or subvert the intended function of the system. Though the problem of malicious code has a long history, a number of recent, widely publicized attacks and certain economic trends suggest that malicious code is rapidly becoming a critical problem for industry, government, and individuals.

Traditional examples of malicious code include viruses, worms, Trojan Horses, and attack scripts, while more modern examples include Java attack applets and dangerous ActiveX controls.
• Viruses are pieces of malicious code that attach to host programs and propagate when an infected program is executed.
• Worms are particular to networked computers. Instead of attaching themselves to a host program, worms carry out programmed attacks to jump from machine to machine across the network.
• Trojan Horses, like viruses, hide malicious intent inside a host program that appears to do something useful (e.g., a program that captures passwords by masquerading as the login daemon.)
• Attack scripts are programs written by experts that exploit security weaknesses, usually across the network, to carry out an attack. Attack scripts exploiting buffer overflows by “smashing the stack” are the most commonly encountered variety.
• Java attack applets are programs embedded in Web pages that achieve foothold through a Web browser.
• Dangerous ActiveX controls are program components that allow a malicious code fragment to control applications.