网络安全-19：恶意软件幻灯片.ppt

第19章作业 写一篇概述计算机恶意软件的小论文。 * 西安电子科技大学计算机学院 * * * This chapter examines malicious software (malware), especially viruses and worms, which exploit vulnerabilities in computing systems. These have been given a lot of (often uninformed) comment in the general media. They are however, of serious concern. * The terminology used for malicious software presents problems because of a lack of universal agreement on all terms and because of overlap. Stallings Table 19.1, and this diagram from 3/e, provide a useful taxonomy. It can be divided into two categories: those that need a host program (being a program fragment eg virus), and those that are independent programs (eg worm); alternatively you can also differentiate between those software threats that do not replicate (are activated by a trigger) and those that do (producing copies of themselves). Will now survey this range of malware. * A backdoor, or trapdoor, is a secret entry point into a program that allows someone that is aware of it to gain access without going through the usual security access procedures. Have been used legitimately for many years to debug and test programs, but become a threat when left in production programs. It is difficult to implement operating system controls for backdoors. Security measures must focus on the program development and software update activities. * A logic bomb is one of the oldest types of program threat, being code embedded in some legitimate program that is set to “explode” when certain conditions, such as the examples shown, are met. Once triggered, a bomb may alter or delete data or entire files, cause a machine halt, or do some other damage. * A Trojan horse is a useful, or apparently useful, program or command procedure (eg game, utility, s/w upgrade etc) containing hidden code that performs some unwanted or harmful function that an unauthorized user could not accomplish directly. Commonly used to make files readable, propagate a virus or worm, or simply to destroy data. *