Rogue security software is a form of computer malware that deceives or misleads users into paying for the fake or simulated removal of malware. Rogue security software, in recent years, has become a growing and serious security threat in desktop computing.

Please view the link below for a list of these fake security programs.
Quoted from: http://en.wikipedia.org/wiki/Rogue_security_software

Trojan Horses are designed to allow a hacker remote access to a target computer system. Once a Trojan horse has been installed on a target computer system, it is possible for a hacker to access it remotely and perform various operations. The operations that a hacker can perform are limited by user privileges on the target computer system and the design of the Trojan horse.
Quoted from: http://en.wikipedia.org/wiki/Trojan_horse_(computing)

Malware, short for malicious software, is software designed to infiltrate a computer system without the owner's informed consent. The expression is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software or program code. The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, including true viruses.

Software is considered malware based on the perceived intent of the creator rather than any particular features. Malware includes computer viruses, worms, trojan horses, most rootkits, spyware, dishonest adware, crimeware and other malicious and unwanted software.
Quoted from: http://en.wikipedia.org/wiki/Malware

Ransomware is computer malware which holds a computer system, or the data it contains, hostage against its user by demanding a ransom for its restoration.
Quoted from: http://en.wikipedia.org/wiki/Ransomware_(malware)

A computer worm is a self-replicating computer program. It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention. This is due to the poor security the computers infected have. Unlike a virus, it does not need to attach itself to an existing program. Worms almost always cause at least some harm to the network, if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.
Quoted from: http://en.wikipedia.org/wiki/Computer_worm

Spyware is a type of malware that is installed on computers and collects information about users without their knowledge. The presence of spyware is typically hidden from the user. Typically, spyware is secretly installed on the user's personal computer. Sometimes, however, spywares such as keyloggers are installed by the owner of a shared, corporate, or public computer on purpose in order to secretly monitor other users.

While the term spyware suggests that software that secretly monitors the user's computing, the functions of spyware extend well beyond simple monitoring. Spyware programs can collect various types of personal information, such as Internet surfing habits and sites that have been visited, but can also interfere with user control of the computer in other ways, such as installing additional software and redirecting Web browser activity. Spyware is known to change computer settings, resulting in slow connection speeds, different home pages, and/or loss of Internet or functionality of other programs. In an attempt to increase the understanding of spyware, a more formal classification of its included software types is captured under the term privacy-invasive software.
Quoted from: http://en.wikipedia.org/wiki/Spyware

Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertisements to a computer after the software is installed on it or while the application is being used. Some types of adware are also spyware and can be classified as privacy-invasive software.
Quoted from: http://en.wikipedia.org/wiki/Adware

A rootkit is a software system that consists of one or more programs designed to obscure the fact that a system has been compromised. Contrary to what its name may imply, a rootkit does not grant a user administrator privileges, as it requires prior access to execute and tamper with system files and processes. An attacker may use a rootkit to replace vital system executables, which may then be used to hide processes and files the attacker has installed, along with the presence of the rootkit. Access to the hardware, e.g., the reset switch, is rarely required, as a rootkit is intended to seize control of the operating system. Typically, rootkits act to obscure their presence on the system through subversion or evasion of standard operating system security scan and surveillance mechanisms such as anti-virus or anti-spyware scan. Often, they are Trojans as well, thus fooling users into believing they are safe to run on their systems. Techniques used to accomplish this can include concealing running processes from monitoring programs, or hiding files or system data from the operating system. Rootkits may also install a "back door" in a system by replacing the login mechanism (such as /bin/login) with an executable that accepts a secret login combination, which, in turn, allows an attacker to access the system, regardless of the changes to the actual accounts on the system.
Quoted from: http://en.wikipedia.org/wiki/Rootkit

A computer virus is a computer program that can copy itself and infect a computer. The term "virus" is also commonly but erroneously used to refer to other types of malware, adware, and spyware programs that do not have the reproductive ability. A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.

The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, adware, and spyware programs that do not have the reproductive ability. Malware includes computer viruses, worms, trojans, most rootkits, spyware, dishonest adware, crimeware, and other malicious and unwanted software, including true viruses. Viruses are sometimes confused with computer worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a program that appears harmless but has a hidden agenda. Worms and Trojans, like viruses, may cause harm to either a computer system's hosted data, functional performance, or networking throughput, when they are executed. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or go unnoticed.
Quoted from: http://en.wikipedia.org/wiki/Computer_virus