Malware or Malicious software is defined as:
A piece of software or program designed to attack, degrade or prevent the intended use of a computer. Types of malware can include viruses, worms, Trojans, malicious active content and denial of service attacks. In the case of invasion of privacy for the purposes of fraud or the theft of identity, software that passively observes the use of a computer is also malware (“spyware”).
The most common ways you get malware from the internet are: