What are cookies?
Cookies (the origin of the name is unknown) offer the option of storing a value on the visitor's computer from a website and reading it out again when visiting the same website again. So it is possible to design a website so that it reacts dynamically to stored values.
Only those cookies can be read that have been set by the website that reads them out.
Thus e.g. Google.de does not read cookies from Yahoo.de.
Viruses are not transmitted using cookies. A cookie is roughly equivalent to an entry in an INI file under the Windows operating system. A variable is saved with an assigned value, for example the date and time of the last visit to the website. Computer data of the user cannot be read out.