Ransomware is a type of malicious software (malware) that encrypts a victim's files or locks their computer, demanding a ransom payment to restore access. It is a form of cyber extortion, where hackers hold the victim's data hostage until a specified amount of money is paid, typically in cryptocurrency.

Once a device is infected with ransomware, the malware encrypts the victim's files, making them inaccessible. The attacker then presents a ransom message, usually in the form of a pop-up or a text file, providing instructions on how to pay the ransom and regain access to the encrypted files or system.

Ransomware attacks are commonly delivered through malicious email attachments, compromised websites, or exploit kits. The encryption process often spreads across networks, affecting multiple devices and shared files. Paying the ransom does not guarantee the safe return of the files, and it can encourage further attacks.