Malware is a software that the user or administrator did not authorize or want on the computer. These malwares are designed to damage, disrupt or gain access to the system. For example, Spyware, grayware, Trojan horses, key loggers, backdoors, rootkits, worms, viruses and more. Once these malwares are installed, it is difficult to detect them by intrusion detection or prevention systems.
Malware can get onto the systems through many different techniques such as, Phishing, Pharming, External Hardware (USB), Social Engineering, Drive-by, Man In The Middle attack (MITM) and more.