What is Malicious Software (Malware)
Malicious Software is a software that is installed on a computer without owner’s approval and can harm the Integrity, Availability and/or Confidentiality of an information system. For instance can steal sensitive information, use computer resources on behalf of the attacker, stop legit processes which are important for the proper operation of the organization.
Malicious Software can be classified in two categories. The first category is the malicious software that needs a legit program to run through and the second category is the malware that can run autonomously.
Furthermore Malicious Software can be classified by its behavior. Such as Virus, Trojans, Rootkits, Worms etc.
Learn More About Phishing
More information about malicious software can be found in the following link.