Adware: A virus which intrusively shows inappropriate or unwanted advertisements.

Anti-virus software: Software that detects malware and other malicious programs. This software can also quarantine and remove suspicious files.

Blacklist: A kind of filter. A list of applications that may not run on a machine or devices that cannot connect to a network. Blacklists exclude only what is on the list. The opposite of a whitelist.

Bluetooth: A technology that allows for short range connections between devices. Often used to connect computers or mobiles to accessories.

Boot sector virus: A virus that inserts itself in a computer's boot sector program, the program your computer runs when you turn it on. These are often spread using portable storage devices, such as a USB stick.

Botnet: A botnet is an illicit network of computers that is created using malware. The controller of a botnet can use a network of many infected computers for different purposes. A computer can be part of a botnet without the user knowing. Botnets are often used to carry out DDoS attacks.

Brute force attacks: A method used to break encryption or guess passwords. This is done by randomly guessing at many solutions very quickly. Modern encryption is mostly invulnerable to this tactic. Some systems will protect users by temporarily locking an account after too many incorrect passwords are entered.

Computer worm: A type of virus designed to spread itself automatically.

Cyberattack: Any deliberate attempt to damage, disrupt, or gain unauthorized access to a computer system.

DDoS: An acronym that stands for Distributed Denial of Service. This is a form of cyberattack, but it is not hacking. A DDoS is used to make a website or server unusable. It does this by overwhelming a server. Often this is done with many thousands of requests to see a page or use a service. Servers can only process requests so fast and as a consequence legitimate requests take a long time to process or may be ignored entirely.

Email virus: A virus that spreads by having people open attachments to emails.

Encryption: A mathematical technique that turns easily read plaintext into difficult to read ciphertext. Turning ciphertext back into plaintext is decryption. Encryption is used mainly to ensure secure communication by making it so only the sender and the intended recipient can use encrypted data.

Firewall: A system that monitors network traffic and either blocks or allows specific traffic according to a set of rules. Firewalls are an essential security feature and can be hardware or software. Firewalls create a barrier between secure private networks or devices and the internet.

Hacking: An attempt to gain unauthorized access or control of a system. Hacking works by taking advantage of different kinds of vulnerabilities. Hackers can exploit unintentional features of software or hardware, people, and network vulnerabilities. 

Hosting service: A company that sells or rents server space to a website.

Internet: The global network of connected computers.

Intranet: A local network of connected computers.

Keylogger virus:  A type of spyware. These viruses record inputs to a computer. For example, the buttons you press on your keyboard. These can be used to steal any information you type into your computer, such as passwords or credit card numbers.

Macro viruses: A virus that is embedded into a program's code. They are often disguised as common files such as word documents.

Malware: A collective term for many different kinds of malicious software. All kinds of computers and devices are potentially vulnerable to malware. Malware can be highly destructive. Anti-virus software can detect and stop many kinds of malware.

Man-in-the-middle attack: This is a type of attack where the attacker covertly inserts themselves as an intermediary between the sender and recipient of information. The attacker passes on the information from the sender to the recipient, but will either steal or alter information. Publicly available wireless networks can be used for this purpose. Many browsers and devices use a verification process to avoid these attacks, however.

Metadata: Information about information. Metadata can describe many facts about information. This can include information about who created the information, if it was sent, where it was sent from, and relationships between pieces of information such as folder structure.

Phishing: A form of social engineering. Phishing is done by sending emails, or other communications, that pretend to be a trusted organization. For example, an email pretending to be from a bank. The purpose of phishing is to trick either a user into opening a file infected with malware or to redirect them to a fraudulent website that collects sensitive information.

Privacy breach: A privacy breach is any unauthorized access, collection, use, or disclosure of personal information. Privacy breaches can be both intentional and unintentional.

Ransomware: A virus designed to prevent a user from accessing data or using a device entirely. Typically this is coupled with a demand for money in exchange for returning control.

Social engineering: A common tactic used by hackers which usually works by taking advantage of people's trust or fear. A hacker may pretend to be someone in order to get their victim to give up sensitive information. The best protection against social engineering is training.

Spyware: A virus that is designed to steal sensitive information or spy on the user. An example of this would be a virus that secretly turns on a web camera.

Trojan virus: Sometimes called a Trojan horse virus. Named after the mythological Trojan horse.  The virus spreads to computers by disguising itself as something useful or innocent.

Virus: Another name for malware. A virus is software designed to do something harmful. Viruses are often designed to spread to other computers.

Whitelist: A kind of filter. A list of applications that may run on a machine or devices that can connect to a network. The opposite of a blacklist (see above).

Wi-Fi: A technology that allows for wireless connection to local networks. Commonly used to connect laptops and mobile devices to the internet.