What is Malicious Software?

Have you ever heard about Trojan Horses? Trojan Horses is a kind of Malicious software.

Malicious software,  another name we called, Malware,  which is used to describe the softwares  access someone's computer system without asking the permission.

There are many types of Malware,  such as spyware, worms and computer viruses. These unwanted software can be caused by person, enterprises and government.

Reference:
"What is Malware?" n.d. In Website Defender. Retrieved March 19, 2014, from 
http://www.websitedefender.com/what-is-malware/