Malware is software that operates on computers and smartphones illegally for the benefit of the malefactor. Malware can collect data, such as logins, passwords and credit card data, use a computer’s resources for calculations (e.g. cryptocurrency mining), spread through a corporate network, etc. There are several most common categories of malicious software. Ransomware encrypts a victim’s computer and demands money for unlocking the device. In some cases, errors in encryption algorithms make decryption impossible although antivirus companies sometimes manage to find a way to restore data without paying a ransom. Currently available methods to restore encrypted data are explained here: https://www.nomoreransom.org/ru/index.html. Still, the most reliable method is backing up data and keeping it in a safe place. Adware is a form of malware that shows ads on an infected computer (for example, it can open extra browser windows whenever a user opens a website). Spyware collects data about the configuration of the victim’s computer, its operating system, etc.