Malware, short for malicious software, is a kind of software that can be installed on a computer without approval from the computer's owner. There are different kinds of malware that can hurt computers, such as viruses and Trojan horses. The term also includes other intentionally harmful programs, such as spyware and ransomware. These programs can steal passwords, delete files, collect personal information, or even stop a computer from working at all. Computer security or anti-malware software is usually good at stopping malware from installing itself. When security software is not installed, malware can get into the computer. Getting rid of malware can be difficult, even when using programs designed to remove it.