Types of Computer Viruses

Malicious Software (Malware)

• Malware is a term that covers viruses, worms, Trojans, and logic bombs, as well as adware and spyware.
• Malware performs actions without the consent or knowledge of the system owner, resulting in a disruptive action or actions.

Categories of Malware

• Malware can consume resources and power on a host system or network.
• Malware can be used to steal information, such as keyloggers.

Viruses

• Viruses are the best-known form of malware.
• Viruses are designed to replicate and attach themselves to other files resident on the system.
• Viruses require some sort of user action to initiate their infectious activities.

Worms

• Worms have the ability to replicate on their own very quickly.
• Worms have been responsible for some of the most devastating denial-of-service attacks known.

Trojan Horses

• Trojan horses rely on social engineering techniques to start infecting a system and causing harm.
• Trojan horses, like viruses, require user action.

Rootkits

• Rootkits can hide within the core components of a system and stay undetected by modern scanners.
• Rootkits are difficult to detect and even more difficult to remove.

Spyware

• Spyware is designed to gather information about a system or a user's activities.
• Spyware may even be set up to infect only files of a certain length or type or that start with a certain letter.

Types of Viruses

• Companion or camouflage viruses compromise a feature of OSs that enables software with the same name, but different extensions, to operate with different priorities.
• Logic bombs are designed to lie in wait until a predetermined event or action occurs.
• File or multipartite viruses infect systems in multiple ways using multiple attack vectors.
• Shell viruses make the infected program into a subroutine that runs after the virus itself runs.
• Cryptoviruses hunt for files or certain types of data on a system and then encrypt it.
• Hoax viruses are designed to make the user take action even though no infection or threat exists.

Worms

• Worms are malware that is entirely self-replicating.
• Worms do not require a host application or user interaction.
• Examples of worms include the SQL Slammer worm (2003).

Adware

• Adware may replace homepages in browsers, place pop-up ads on a user's desktop, or install items on a victim's system that are designed to advertise products or services.

Virus Creation Process

• The creation process involves design, replication, launch, detection, incorporation, and elimination.

Examples of Viruses

• The Wabbit virus (mid-1970s) was a replication virus.
• The Elk Cloner (1982) was a rapidly spreading virus.
• The first PC-compatible virus (1986) infected the boot sector.
• The Jerusalem virus (1987) was the first logic bomb, which debuted on Friday the 13th.
• Polymorphic viruses (1992) were designed to change their code and shape to avoid detection.