Malware
Malware is any software intentionally designed to cause disruption to a computer, server, client, or computer network, leak private information, gain unauthorized access to information or systems, deprive access to information, or which unknowingly interferes with the user's computer security and privacy. Researchers tend to classify malware into one or more sub-types.
Malware poses serious problems to individuals and businesses on the Internet. According to Symantec's 2018 Internet Security Threat Report, malware variants number has increased to 669,947,865 in 2017, which is twice as many malware variants as in 2016. Cybercrime, which includes malware attacks as well as other crimes committed by computer, was predicted to cost the world economy US$6 trillion in 2021, and is increasing at a rate of 15% per year. Since 2021, malware has been designed to target computer systems that run critical infrastructure such as the electricity distribution network.
The defense strategies against malware differ according to the type of malware but most can be thwarted by installing antivirus software, firewalls, applying regular patches, securing networks from intrusion, having regular backups and isolating infected systems. Malware can be designed to evade antivirus software detection algorithms.
History
The notion of a self-reproducing computer program can be traced back to initial theories about the operation of complex automata. John von Neumann showed that in theory a program could reproduce itself. This constituted a plausibility result in computability theory. Fred Cohen experimented with computer viruses and confirmed Neumann's postulate and investigated other properties of malware such as detectability and self-obfuscation using rudimentary encryption. His 1987 doctoral dissertation was on the subject of computer viruses. The combination of cryptographic technology as part of the payload of the virus, exploiting it for attack purposes was initialized and investigated from the mid-1990s, and includes initial ransomware and evasion ideas.Before Internet access became widespread, viruses spread on personal computers by infecting executable programs or boot sectors of floppy disks. By inserting a copy of itself into the machine code instructions in these programs or boot sectors, a virus causes itself to be run whenever the program is run or the disk is booted. Early computer viruses were written for the Apple II and Mac, but they became more widespread with the dominance of the IBM PC and MS-DOS. The first IBM PC virus in the wild was a boot sector virus dubbed Brain, created in 1986 by the Farooq Alvi brothers in Pakistan. Malware distributors would trick the user into booting or running from an infected device or medium. For example, a virus could make an infected computer add autorunnable code to any USB stick plugged into it. Anyone who then attached the stick to another computer set to autorun from USB would in turn become infected, and also pass on the infection in the same way.
Older email software would automatically open HTML email containing potentially malicious JavaScript code. Users may also execute disguised malicious email attachments. The 2018 Data Breach Investigations Report by Verizon, cited by CSO Online, states that emails are the primary method of malware delivery, accounting for 96% of malware delivery around the world.
The first worms, network-borne infectious programs, originated not on personal computers, but on multitasking Unix systems. The first well-known worm was the Morris worm of 1988, which infected SunOS and VAX BSD systems. Unlike a virus, this worm did not insert itself into other programs. Instead, it exploited security holes in network server programs and started itself running as a separate process. This same behavior is used by today's worms as well.
With the rise of the Microsoft Windows platform in the 1990s, and the flexible macros of its applications, it became possible to write infectious code in the macro language of Microsoft Word and similar programs. These macro viruses infect documents and templates rather than applications, but rely on the fact that macros in a Word document are a form of executable code.
Many early infectious programs, including the Morris Worm, the first internet worm, were written as experiments or pranks. Today, malware is used by both black hat hackers and governments to steal personal, financial, or business information. Today, any device that plugs into a USB port – even lights, fans, speakers, toys, or peripherals such as a digital microscope – can be used to spread malware. Devices can be infected during manufacturing or supply if quality control is inadequate.
Purposes
Since the rise of widespread broadband Internet access, malicious software has more frequently been designed for profit. Since 2003, the majority of widespread viruses and worms have been designed to take control of users' computers for illicit purposes. Infected "zombie computers" can be used to send email spam, to host contraband data such as child pornography, or to engage in distributed denial-of-service attacks as a form of extortion. Malware is used broadly against government or corporate websites to gather sensitive information, or to disrupt their operation in general. Further, malware can be used against individuals to gain information such as personal identification numbers or details, bank or credit card numbers, and passwords.Beyond its use in criminal enterprises, malware has also been deployed as a tool for sabotage, often driven by political objectives. A notable example is Stuxnet, which was engineered to interfere with specific industrial control systems.
In other cases, politically motivated malware attacks have targeted entire networks, causing widespread disruption. These incidents have included the mass deletion of files and damage to master boot records—actions sometimes described as "computer killing." High-profile examples include the attack on Sony Pictures Entertainment in November 2014, which involved malware known as Shamoon, and a similar strike against Saudi Aramco in August 2012.
In 2024, a botnet owner was arrested for engaging in a pay-per-install operation for financial gain.
Types
Malware can be classified in numerous ways, and certain malicious programs may fall into two or more categories simultaneously. Broadly, software can categorised into three types: goodware; grayware and malware.| Type | Characteristics | Examples |
| Goodware | Obtained from trustworthy source | |
| Grayware | Insufficient consensus or metrics | |
| Malware | Broad consensus among antivirus software that program is malicious or obtained from flagged sources. |
Malware
Virus
A computer virus is software usually hidden within another seemingly harmless program that can produce copies of itself and insert them into other programs or files, and that usually performs a harmful action. They have been likened to biological viruses. An example of this is a portable execution infection, a technique, usually used to spread malware, that inserts extra data or executable code into PE files. A computer virus is software that embeds itself in some other executable software on the target system without the user's knowledge and consent and when it is run, the virus is spread to other executable files.Worm
A worm is a stand-alone malware software that transmits itself over a network to infect other computers and can copy itself without infecting files. These definitions lead to the observation that a virus requires the user to run an infected software or operating system for the virus to spread, whereas a worm spreads itself.Rootkits
Once malicious software is installed on a system, it is essential that it stays concealed, to avoid detection. Software packages known as rootkits allow this concealment, by modifying the host's operating system so that the malware is hidden from the user. Rootkits can prevent a harmful process from being visible in the system's list of processes, or keep its files from being read.Some types of harmful software contain routines to evade identification or removal attempts, not merely to hide themselves. An early example of this behavior is recorded in the Jargon File tale of a pair of programs infesting a Xerox CP-V time sharing system:
Backdoors
A backdoor is a broad term for a computer program that allows an attacker persistent unauthorised remote access to a victim's machine often without their knowledge. The attacker typically uses another attack to bypass authentication mechanisms usually over an unsecured network such as the Internet to install the backdoor application. A backdoor can also be a side effect of a software bug in legitimate software that is exploited by an attacker to gain access to a victim's computer or network.The idea has often been suggested that computer manufacturers preinstall backdoors on their systems to provide technical support for customers, but this has never been reliably verified. It was reported in 2014 that US government agencies had been diverting computers purchased by those considered "targets" to secret workshops where software or hardware permitting remote access by the agency was installed, considered to be among the most productive operations to obtain access to networks around the world. Backdoors may be installed by Trojan horses, worms, implants, or other methods.
Trojan horse
A Trojan horse misrepresents itself to masquerade as a regular, benign program or utility in order to persuade a victim to install it. A Trojan horse usually carries a hidden destructive function that is activated when the application is started. The term is derived from the Ancient Greek story of the Trojan horse used to invade the city of Troy by stealth.Trojan horses are generally spread by some form of social engineering, for example, where a user is duped into executing an email attachment disguised to be unsuspicious,, or by drive-by download. Although their payload can be anything, many modern forms act as a backdoor, contacting a controller which can then have unauthorized access to the affected computer, potentially installing additional software such as a keylogger to steal confidential information, cryptomining software or adware to generate revenue to the operator of the trojan. While Trojan horses and backdoors are not easily detectable by themselves, computers may appear to run slower, emit more heat or fan noise due to heavy processor or network usage, as may occur when cryptomining software is installed. Cryptominers may limit resource usage or only run during idle times in an attempt to evade detection.
Unlike computer viruses and worms, Trojan horses generally do not attempt to inject themselves into other files or otherwise propagate themselves. Modern Trojans are often disguised within legitimate-looking applications, making them particularly effective at bypassing basic user awareness and simple antivirus measures.
In spring 2017, Mac users were hit by the new version of Proton Remote Access Trojan trained to extract password data from various sources, such as browser auto-fill data, the Mac-OS keychain, and password vaults.