Malware (a portmanteau for malicious software) is any software intentionally designed to cause damage to a computer, server, client, or computer network. Malware does the damage after it is implanted or introduced in some way into a target's computer and can take the form of executable code, scripts, active content, and other software. The code is described as computer viruses, worms, Trojan horses, ransomware, spyware, adware, and scareware, among other terms. Malware has a malicious intent, acting against the interest of the computer user—and so does not include software that causes unintentional harm due to some deficiency, which is typically described as a software bug.
Programs officially supplied by companies can be considered malware if they secretly act against the interests of the computer user. For example, Sony sold the Sony rootkit, which contained a Trojan horse embedded into CDs that silently installed and concealed itself on purchasers' computers with the intention of preventing illicit copying. It also reported on users' listening habits, and unintentionally created vulnerabilities that were then exploited by unrelated malware.One strategy for protecting against malware is to prevent the malware software from gaining access to the target computer. For this reason, antivirus software, firewalls and other strategies are used to help protect against the introduction of malware, in addition to checking for the presence of malware and malicious activity and recovering from attacks.