Malware, short for malicious software, is any software used to disrupt computer or mobile operations, gather sensitive information, gain access to private computer systems, or display unwanted advertising.

Before the term malware was coined by Yisrael Radai in 1990, malicious software was referred to as computer viruses.

The first category of malware propagation concerns parasitic software fragments that attach themselves to some existing executable content.

The fragment may be machine code that infects some existing application, utility, or system program, or even the code used to boot a computer system.

Malware is defined by its malicious intent, acting against the requirements of the computer user, and does not include software that causes unintentional harm due to some deficiency.

Computer hardware is the collection of physical components that constitute a computer system.

Computer hardware is the physical parts or components of a computer, such as monitor, keyboard, computer data storage, graphic card, sound card, motherboard, and so on, all of which are tangible objects.

By contrast, software is instructions that can be stored and run by hardware.

A computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) or infecting other computer programs by modifying them.

Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive.

When this replication succeeds, the affected areas are then said to be "infected" with a computer virus.

The term "virus" is also commonly, but erroneously, used to refer to other types of malware.

"Malware" encompasses computer viruses along with many other forms of malicious software, such as computer "worms", ransomware, trojan horses, keyloggers, rootkits, spyware, adware, malicious Browser Helper Object (BHOs) and other malicious software.

The majority of active malware threats are actually trojan horse programs or computer worms rather than computer viruses.

The term computer virus, coined by Fred Cohen in 1985, is a misnomer.

Viruses often perform some type of harmful activity on infected host computers, such as acquisition of hard disk space or central processing unit (CPU) time, accessing private information (e.g., credit card numbers), corrupting data, displaying political or humorous messages on the user's screen, spamming their e-mail contacts, logging their keystrokes, or even rendering the computer useless.

However, not all viruses carry a destructive "payload" and attempt to hide themselves—the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without user consent.

Computer software, or simply software, is that part of a computer system that consists of data or computer instructions, in contrast to the physical hardware from which the system is built.

In computer science and software engineering, computer software is all information processed by computer systems, programs and data.

Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media.

Computer hardware and software require each other and neither can be realistically used on its own.

In computing, Trojan horse, or Trojan, is any malicious computer program which is used to hack into a computer by misleading users of its true intent.

The term is derived from the Ancient Greek story of the wooden horse that was used to help Greek troops invade the city of Troy by stealth.