Internet hacks and attacks are part of an ever-changing, ever-expanding industry that hopes to fool or exploit PC users. The best defense against such threats is education. We've created a glossary of the most common terms relating to Internet security to help CNET users navigate the dangers from A to Z.

A | B | C | D | E | F | H | K | M | P | R | S | T | V | W | Z

ActiveX Controls

These controls link to any object--traditionally dynamic content such as tables and buttons that react to mouse clicks--embedded within a Web page. Although ActiveX controls help Web pages spring to life, malicious programmers can easily use them as vehicles for downloading spyware. Install a sturdy browser and firewall that screens your ActiveX Controls, and download them with care, accepting ActiveX only from trusted Web sites.

Adware

Typically, adware components install alongside a shareware or freeware application. These advertisements create revenue for the software developer and are provided with initial consent from the user. Adware displays Web-based advertisements through pop-up windows or through an advertising banner that appears within a program's interface.

Antispyware software

This is a broad term for programs designed to protect a computer from adware and spyware. Almost all antispyware applications feature a scanning engine, which detects suspicious items and removes them from the infected machine. Some antispyware applications also include a real-time-protection module, a shield that alerts users when suspicious programs attempt to install themselves and allows users to deny them.

Backdoor programs

This refers to any software program that allows other users to control machines remotely while hiding any evidence of the fact. Software developers are the most common authors and users of backdoor programs, adding them to make testing easier. Backdoor Trojan horses are spyware programs that sabotage your PC. These specific Trojan horses force a backdoor program onto your machine and infiltrate your system to collect information or install spyware.

Bot

An Internet robot, shortened to "bot," is an automated program that performs a specific timesaving function in lieu of a human operator, such as a spider that trolls Web sites collecting data for market research. Spyware bots secretly install through worms, Trojan horses, and drive-by downloads. They are mostly used to carry out remote attacks, such as denial-of-service (DoS) attacks.

Botnet

A botnet is a network of bots installed on multiple computers, each running identical malware. A botnet can be controlled remotely via an IRC (Internet Relay Chat) server or a peer-to-peer application.

Browser-helper object (BHO)

BHOs are files--most frequently DLLs--that add additional functionality to Internet Explorer. Although many useful programs such as Adobe Acrobat employ BHOs, these files also can be used for unsavory purposes. BHOs associated with adware or spyware can monitor your browsing activities, hijack your home page, or replace certain advertisements with others.

Cracker

Cracker is a shortened name for a criminal hacker. Read more at hacker.

Denial-of-service (DoS) attack

Denial of service is an attack designed to block user access to a Web site or network by flooding it with bogus information (such as a surplus of requests). The information overload maxes out the Web site or network's processing capabilities, resulting in the user's inability to access Internet services and making it appear inaccessible. These DoS attacks damage productivity and can be highly frustrating, though the hacker's primary purpose of such attacks is generally disruption and not identity theft.

Distributed denial-of-service (DDoS) attack

This variety of DoS attack enlists multiple compromised computers to flood a single target with bogus information. A criminal hacker can hijack your computer and force it and others to perform a DoS attack against other computers, users, or networks.

Dialer

Traditional modems use a program called a dialer to connect a computer to the Internet, but dialers are perhaps most well-known for their illegitimate purposes. Bad dialers cause your PC to call long-distance or for-pay numbers, rather than your ISP. This most often results in a large telephone bill for the user and a tidy profit for the dialer's creator.

Drive-by

This term is loosely used for a stealth software installation the user does not initiate. In some cases, simply visiting a Web page can download malicious programs to a PC without a user's knowledge or consent. In other cases, a pop-up ad might be used to initiate a drive-by installation.

Evil twin

A spoofed doppelganger of a legitimate wireless access point is known as an evil twin. Often home constructed, the evil twin hotspot offers wireless access for the purpose of collecting the user's data, which can then be exploited or sold.

False positive

False positives can fall into several categories. In an effort to sell software, unscrupulous antispyware programs often will mislead a user into believing his or her machine is infected with spyware when no problems actually exist. The term false positive also can be used when legitimate antispyware applications mistakenly label a benign program as a threat.

Firewall

A firewall is a crucial component in a computer's line of defense, as firewalls prevent unauthorized services or programs from accessing a computer or network resources. Although virtually every corporate network has its own firewall, every personal computer should have one as well. Personal firewalls can come as standalone products or as components built-in to a larger security suite.

Hacker

"Hacker" is a term that often requires more qualification than is given, as hackers can act with intentions and outcomes ranging from beneficial to malicious. To hack a file or a program is simply to deconstruct it or tweak its performance. Therefore the term hacker has neutral connotations, encompassing those who tinker with computer programs with no malicious intent, such as computer programmers or security researchers, as well as criminal hackers (also called crackers) who seek to damage your system, gain from stored data, or control your PC remotely. Hacking taxonomy is associated by color--black hat hackers are malicious, white hat hackers are benign, and gray hat hackers are characterized by varying motivations.

Hijackers

Often installing as a helpful browser toolbar, hijackers may alter browser settings or change the default home page to point to some other site.

Keylogger

Keyloggers are just what they sound like--programs that record every keystroke made on a PC. Though some parental-control applications include keyloggers for monitoring purposes, the ones that come bundled with spyware are far more insidious. These types of keyloggers send sensitive information to a remote computer, where thieves can access data such as credit-card and bank-account numbers, as well as passwords and social-security numbers.

Malware

Malware is generally used to describe a piece of software that exploits or inconveniences the user. It usually refers to the most malicious forms of adware and spyware.

Man-in-the-middle attack

In this particular type of attack, a third party piggybacks on valid user privileges to gain unapproved access to a computer or network. The man-in-the-middle (MITM) attack exploits the authentication process of a one-way authentication (user approved by the network) wireless access point (WAP). MITM attacks are orchestrated by intercepting a valid authentication granted by a network with a one-way authentication setup to any valid Media Access Connection (MAC). With the user's legitimate access as a shield, the MITM has full access to the data flowing in and out of a user's computer.

Pharming

Like phishing, pharming preys on socially conditioned patterns of human behavior to coax sensitive information from victims. Whereas phishers masquerade as legitimate organizations, pharmers hijack sites' domain names to redirect traffic elsewhere. In this way, visitors to an online banking site can be channeled to a mirror site and prompted to provide personal data that crackers can collect and use.

Phishing

Spoofing legitimate organizations to lure users into giving up sensitive data is a favorite technique among security fraudsters. In a common phishing scam, users receive a look-alike e-mail message purportedly from a trusted institution like their bank, alerting them to an urgent need. Users follow the embedded link to a convincing site that requires them to sign in using account information.

Among the subsets of phishing scams, spear phishing targets a specific user demographic, such as gamers. In VoIP phishing, users are directed to verify their account information over the phone rather than on a Web site.

Phreaking

Combining the words "phone" and "freak," phreaking refers to a wide subculture of hacking that involves manipulating and exploiting telephone systems.

Rogue antispyware software

Posing as legitimate antispyware applications, these malicious programs scan a computer and induce false positives to scare users into buying a product. Rogues often attempt to distribute themselves via ominous pop-up ads and can be very difficult to manually uninstall.

Rootkit

Although an exact definition of what constitutes a rootkit is still under debate, it is generally regarded as a piece of software that allows intruders to conceal malicious files and programs from users or system administrators. Rootkits can be extremely hard to uninstall and allow troublemakers to go about their dirty work undetected.

Spam

Originally, the unsolicited bulk messages that inundate a user's account took the form of e-mail messages (mostly advertisements) in which the sender attempted to engage the user in a purchase. Spam has evolved, and unsolicited bulk messages crop up in instant messages (spim), blog comments (splogs), mobile texts (SMS spam), forums, and so on. More than merely annoying, spam attachments can contain viruses and malware or link to dangerous Web sites. Spam is the principle vehicle for phishing scams.

Spoof

Spoofs are misleading Web addresses, spam e-mails, and IP addresses forged by a malicious hacker to look identical to the legitimate organization's materials. They are used to trick users into responding to alerts that appear to be issued by trusted organizations such as banks. Users who respond to the visual fakery and urgency of the requests are prompted to give up private data, which is then often used in identity theft. Spoofs are instrumental in carrying out phishing, pharming, and phreaking scams.

In a pharming exploit, a spoofed IP address of a legitimate company might be scripted to float over the culprit's actual, nonlegitimate IP address in order to make the user believe the site is valid.

Spyware

Spyware refers to programs that gather and transmit the user's personal details or behavior to a third party, often without the user's knowledge or consent. Like adware, it often installs as a third-party component bundled with freeware or shareware, creating a fuzzy distinction between the two.

Tracking cookies

Internet browsers write and read cookies, files with small amounts of data (such as site passwords and settings) based on instructions from Web sites. In many cases, cookies provide a benefit to users. However, in some instances cookies are used to consolidate and track user behavior across different sites, which provides marketers with private information about an individual.

Trojan horses

Trojan horses slip into an individual's system and run without the user's knowledge. They can have many functions. For example, some use a computer's modem to dial long-distance, generating huge phone bills for the computer owner. Unlike viruses and worms, Trojan horses do not make copies of themselves.

Virus

Like human viruses, the computer varieties contain harmful code and spread easily to infect multiple hosts. Viruses are notorious for corrupting hardware, software, and personal files. Viruses cannot spread on their own, requiring users to share infected files through e-mail attachments, flash drives, disks, P2P, Web sites, or any other file-transferring mechanisms.

Worm

Often conflated with viruses, worms also are self-replicating programs; however, they propagate independently of user interaction, often through a shared or direct network connection. Worms may destroy data on individual machines, but mostly inflict their damage by siphoning users' bandwidth or shutting down their computers.

Zombie

Using viruses, Trojan horses, and worms, criminal hackers can remotely operate a compromised machine without the knowledge of its owner. Zombie computers often host programs that allow them to be conscripted by a remote controller into bot armies, called botnets, to launch DDoS attacks.

Zero-day exploit

Malicious hackers have discovered they can increase their level of destruction by cracking the defenses of a product on the same day that news of a vulnerability breaks and/or an ensuing patch is released. Disclosure practices compel software and security vendors to publicly announce flaws, which informs fast-acting exploiters. The resulting zero-day attacks affect users who haven't applied a patch to fix the vulnerability.