Malware: Malware, short for malicious software, consists of programming (code, scripts, active content, and other software) designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, gain unauthorized access to system resources, and other abusive behavior.
A few examples of malware:
1. Virus: A computer program that can copy itself and infect a computer.
2. Worm: A self-replicating malware computer program, which uses a computer network to send copies of itself to other computers on the network.
3. Spyware: A malware that collects small pieces of information about users without their knowledge.
4. Adware: Any software package which automatically plays, displays, or downloads advertisements to a computer.
5. Trojan horse: A destructive program that masquerades as an application. The software initially appears to perform a desirable function for the user prior to installation, but steals information or harms the system.
6. Rootkits: Once a malicious program is installed on a system or a human attacker breaks into a computer, it is essential that it stays concealed, to avoid detection and disinfection. Techniques known as rootkits allow this concealment, by modifying the host's operating system so that the malware is hidden from the user. Rootkits can prevent a malicious process from being visible in the system's list of processes, or keep its files from being read.
7. Backdoors: It is a method of bypassing normal authentication procedures. Once a system has been compromised (by one of the above methods, or in some other way), one or more backdoors may be installed in order to allow easier access in the future. Backdoors may also be installed prior to malicious software, to allow attackers entry.