# Malware ## What is Malware Malware is a broad term for malicious software, meaning any software intentionally designed to cause damage to a computer, server, network, or user. Malware is created by attackers to steal data, spy on users, disrupt operations, hold data for ransom, use infected machines for further attacks, or simply cause damage. Malware is distributed through email attachments, malicious websites, infected software downloads, USB drives, and network exploits. Understanding different types of malware helps in defending against them. ## Viruses A computer virus is a type of malware that attaches itself to legitimate programs or files and spreads when the infected file is executed or shared. Like biological viruses, computer viruses replicate by inserting copies of themselves into other programs. When an infected program is run, the virus code executes and may infect other programs, display messages, delete files, or perform other malicious actions. Viruses require user action to spread, such as opening an infected email attachment or running an infected program. ## Worms Worms are similar to viruses in that they self-replicate, but they spread through network connections without requiring user action. A worm exploits vulnerabilities in network services to spread from one system to another automatically. The Morris Worm of 1988 was one of the first internet worms. Modern worms can spread across the internet infecting thousands of systems within minutes. Worms can cause significant network congestion and system disruption even if their payload performs no intentional damage. ## Ransomware Ransomware is malware that encrypts the victim's files and demands payment, typically in cryptocurrency, in exchange for the decryption key. Ransomware attacks have become increasingly common and damaging. Attackers typically demand thousands to millions of dollars. Some ransomware groups operate as ransomware-as-a-service, developing the malware and infrastructure and selling access to criminal affiliates who conduct the attacks. Hospitals, municipalities, schools, and large corporations have been seriously disrupted by ransomware attacks. Effective backups that are not connected to the main network are the most important defense. ## Trojans A Trojan horse, or simply Trojan, is malware disguised as legitimate software. The victim installs what appears to be useful software, but the software secretly performs malicious actions. Trojans may create backdoors allowing remote access, steal credentials, log keystrokes, or download additional malware. Remote Access Trojans, or RATs, give attackers complete remote control over infected systems. ## Spyware and Adware Spyware monitors user activity and sends information to the attacker without the user's knowledge. Keyloggers record all keystrokes, capturing passwords and other sensitive data. Screen capture spyware periodically takes screenshots. Adware displays unwanted advertisements and may track browsing behavior.