How does a virus work?

Again and again one reads of new PC viruses on the Internet. But very few users know how such a virus works at all. We clarify it.

What is a virus and how does it work?

A virus is a subset of the so-called "malware". This refers to computer programs that want to harm the user.

• Definition: A virus usually consists of just one file that can be executed as a program. With a small code, otherwise harmless files can also be converted into viruses. In general, viruses have the task of penetrating a system unnoticed and causing damage to the user or profit from espionage for the virus manufacturer.
• Types: There are numerous types of viruses. They differ not only in the targeted point of attack, but also in the way they work and the file types they are in.
• Infection routes: Viruses most often enter the system via the browser and e-mails. If you enter seemingly harmless search terms in Google, you will often end up on websites that initially infect your computer without being noticed. Viruses are just as common in email attachments. For example, thousands of users receive fake invoice emails every day. Viruses are hidden here in attachments or links.
• How it works: Unlike "worms", classic viruses cannot carry out themselves, which is why they are less common these days (see picture). If a virus is actively started by the user or if he has nested in another program and is started via this, the consequences are very different. If the virus remains undetected, it can do just about anything, from harmless changes to the system, through deletion processes, to hardware damage.
• File types: In general, you cannot be sure that a file is virus-free. Codes that act as viruses can even be written unnoticed in photos. Therefore, you should not open files whose origin you do not know.
• Protection: No computer can be fully protected against viruses unless it is never connected to the Internet or external storage media such as USB sticks. Otherwise, anti-virus protection is essential. Although it cannot detect and stop all threats, its detection rate is relatively high. Popular free programs are the products from avast, Avira, Microsoft and AVG.
• Limitation of damage: Once a virus has made it onto your computer, it is extremely difficult to remove it. Often it is not enough to just delete the original file. In an emergency, you should reinstall the operating system to completely clean the system.

In this practical tip, you can read how to recognize a Trojan on your computer.