Sniffer
A sniffer is a program that monitors and analyzes network traffic, detecting bottlenecks and problems.
Using this information, a network manager can keep traffic flowing efficiently.
A sniffer can also be used illegitimately to capture data being transmitted on a network. A network router reads every packet of data passed to it, determining whether it is intended for a destination within the router's own network or whether it should be passed further along the Internet. A
router with a sniffer, however, may be able to read the data in the packet as well as the source and destination addresses.
The term "sniffer" is occasionally used for a program that analyzes data other than network traffic. For example, a database could be analyzed for certain kinds of duplication.
A number of companies offer products that include "Sniffer" as part of their name. Network Associates offers a suite of Sniffer products that monitor and analyze different kinds of networks.
Hacker
The term hacker usually means someone who attempts to break into computer systems. Typically, this kind of hacker would be a proficient programmer or engineer with sufficient technical knowledge to understand the weak points in a security system.
Nuking
blue bomb (WinNuke or nuking)
A "blue bomb" (also known as "the blue screen of death" or "WinNuke") is a technique for causing the Windows operating system of someone you're communicating with to crash or suddenly terminate .The "blue bomb" is actually an out-of-band network packet containing information that the operating system can't process. This condition causes the operating system to "crash" or terminate prematurely. The operating system can usually be restarted without any permanent damage other than possible loss of unsaved data when you crashed.
The blue bomb derives its name from the effect it sometimes causes on the display as the operating system is terminating - a white-on-blue error screen. Blue bombs are sometimes sent by multi-player game participants who are about to lose or users of Internet Relay Chat (IRC) who are making a final comment. This is known as "nuking" someone. A commonly-used program for causing the blue bomb is WinNuke. Many Internet service providers are filtering out the packets so they don't reach users.
Trojan Horse
A Trojan horse is defined by FOLDOC as a "malicious, security-breaking program that is disguised as something benign" such as a screen saver, game, hack, nuke, etc. Instead, running the file gives control of your computer over to somebody else, who can now takeover your IRC channels, steal account passwords, modify/erase files on your disk, use your computer to perform felonious denial of service attacks on others, or worse! Trojans are not the same as viruses, but once you're "infected", the effects are just as dangerous, and you can spread the trojan to others without even being aware of it!
Trojans are typically files with suffices like "ini", "exe", or "com", such as "dmsetup.exe". These days nearly all trojans are spread in the guise of a free game or other software. You probably downloaded one from a WWW or FTP archive, ICQ file exchange, or through IRC's DCC file transfer (by manual /dcc get or, worst yet, an "auto DCC get" feature which allows anybody to send you anything, including not only trojans but also viruses, child porn, etc.). Typically the trojan needs to be run manually, and installs hacked files all over your disk silently.
Worm
Perhaps the best-known example was the Great Worm.
The November 1988 worm perpetrated by Robert T. Morris. The worm was a program which took
advantage of bugs in the Sun Unix sendmail program, Vax programs, and other security loopholes to distribute itself to over 6000 computers on the Internet. The worm itself had a bug which made it create many copies of itself on machines it infected, which quickly used up all available processor time on those systems.
Virus
In the 1990s, viruses have become a serious problem, especially among IBM PC and Macintosh users (the lack of security on these machines enables viruses to spread easily, even infecting the operating system). The production of special antivirus software has become an industry, and a number of exaggerated media reports have caused outbreaks of near hysteria among users; many users tend to blame *everything* that doesn't work as they had expected on virus attacks. Accordingly, this sense of "virus" has passed into popular usage (where it is often incorrectly used to denote a worm or even a Trojan horse).
A cracker program that searches out other programs and "infects" them by embedding a copy of itself in them, so that they become Trojan horses. When these programs are executed, the embedded virus is executed too, thus propagating the "infection". This normally happens invisibly to the user.
Unlike a worm, a virus cannot infect other computers without assistance. It is propagated by vectors such as humans trading programs with their friends . The virus may do nothing but propagate itself and then allow the program to run normally. Usually, however, after propagating silently for a while, it starts doing things like writing "cute" messages on the terminal or playing strange tricks with the display (some viruses include display hacks). Many nasty viruses, written by particularly antisocial crackers, do irreversible damage, like deleting all the user's files.