What is a computer virus?
A computer virus is capable of replicating itself independently. It infects a host file, a document, a program, the boot sector of a data carrier, or memory areas of a computer and deposits its program code there. If the file, program, or memory area is accessed, the program code is also executed.
The functions of a virus are manifold. It can change the way the computer works and usually has harmful effects. For example, the virus deletes files, prevents the operating system from running, or, in extreme cases, damages the hardware. Viruses, like worms, Trojans, or ransomware, belong to the malware category.
Differentiation from other types of malware such as worms or Trojans
The term computer virus is often used as an umbrella term for all malware that can infect a computer. This is incorrect, as a computer virus is only a specific type of malware and the term virus refers to infection using a host file. Other malware, such as Trojans or worms, are not strictly speaking computer viruses, as they use other infection or replication mechanisms and are conceptually different.
While a virus requires a host program, worms spread autonomously. Once a worm has managed to penetrate a system, it creates copies of itself and actively attempts to infect other systems over the network. Worms spread over the Internet or a network by exploiting security holes and vulnerabilities without requiring a user to copy infected host files onto a system.
A Trojan is a malware that is hidden in software. The software pretends to be a normal application and tricks the user into performing certain functions. In the background, it opens the system to other malware. In principle, a Trojan can be used to infect any malicious code.
Viruses infection routes
Initially, removable media such as floppy disks or CDs were the main infection routes for viruses. With the increased use of networks and the Internet, viruses use email attachments, download files, or share documents on a network drive to infect. USB storage devices are also typical infection routes for computer viruses.
Types of computer viruses
Typical types of computer viruses are:
- Email viruses in the form of infected file attachments.
- Software viruses in the form of infected download files
- Boot sector viruses in the form of infected boot sectors of hard disks, removable disks, or floppy disks
- Macro viruses in the form of documents with infected macros
- Protective measures against computer viruses
Since a computer virus requires a host program to infect and spread, the most important protective measure is the careful handling of foreign files, software, file attachments, or removable media. Files should be scanned by an anti-virus program before saving or running them on a computer. Downloading files from untrustworthy sources should be avoided altogether.
Other measures to protect against malware include regularly updating the operating system and applications, working with restricted user rights, blocking the automatic opening of files from the Internet, deactivating the automatic start of macros, or disabling the auto-start function for removable media.