Numerous types of cyber threats or system intrusions exist. Some are very dangerous and disruptive; others are just a nuisance. The most common types of cyber threats include: • Adware programs that covertly gather personal information of online users and relay it to another computer, often for advertising objectives. This kind of information gathering is often done by tracking information related to Internet browser habits. • Adware downloaded from Websites, usually in the form of freeware. Thus, a user wanting freeware may unknowingly trigger adware by accepting the terms found in an End-User Licensing Agreement from a software program that just happens to be linked to the adware. • Dialer programs using a system to connect to the Internet by calling a 900 number or by calling to an FTP site without authorization by the user. • Crack tools giving unauthorized access to another’s computer, as with a keystroke logger, a software program capable of tracking and recording a user’s keystrokes and then sending this data to the cracker. • Hoaxes or emails sent along the Internet in a chain-letter fashion with the purpose of trying to scare users by describing a devastating (but unlikely) virus that has infected their machine, a form of extortion. • Joke programs altering or disrupting the normal activities of a computer by harmlessly creating a nuisance, such as putting on some unexpected screen saver. • Remote access tools permitting another system to gather data or to attack or alter someone’s computer or the files contained therein, usually over the Internet. • Spyware, a stand-alone program that monitors a system’s activities, detecting passwords and other confidential information without being detected, and sends this information to another computer. • Trojan horses, software programs (often arriving in a joke program) that do not replicate or copy themselves but can and often do cause considerable system damage or compromise the system’s security. • Virus, code that not only replicates itself but also infects another program, a boot sector, a partition sector, or a document with executable instructions (such as macros) by attaching itself or inserting itself into that medium. Although most viruses just replicate and do little more, others can cause a significant amount of damage. • Worms, programs that make copies of themselves and infect other computer systems, typically without a user’s action, exploiting vulnerabilities in operating system or application software. Worms can compromise the security of the computer and cause considerable damage. Schell, B.H. and Martin, C. Contemporary World Issues Series: Cybercrime: A Reference Handbook. Santa Barbara, CA: ABC-CLIO, 2004; Symantec Security Response. Glossary. [Online, July 15, 2004.] Symantec Security Response Website. http://securityresponse.symantec .com/avcenter/refa.html.