Computer viruses are a subspecies of malware. While a real virus needs a host cell to spread, a computer virus needs files or documents to multiply within a computer. This way, the virus creates copies of itself in uninfected files and can infect other computers via networks or external devices when users copy an infected file.
A virus can attach itself to program files, scripts or documents with macros,remaining inactive and hidden until certain conditions are met that trigger execution. The damage caused by viruses is manifold. It ranges from harmless disturbances such as a slow computer, constant pop-ups and non-functioning applications, to data theft, data loss, or even hardware damage.
Viruses spread via removable storage media such as USB sticks or other storage media which as they are intentionally designed to be connected to a computer. However, infected downloads, e-mail attachments, fake links, or instant messages with executable files can also contain viruses or other forms of malware. Criminals also like to exploit vulnerabilities in outdated software to spread their malware.
Viruses have now almost completely been replaced by worms. This is because viruses have to be actively copied into a new system by a user, whereas worms search for vulnerabilities and exploit them independently. Since almost every device is connected to the Internet or a local network, this benefits the active distribution strategy of worms.
