Cache - A special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.
Captcha - A challenge-response test that determines whether a user is human or an automated bot.
Card skimmers - An illegal electronic device that captures personal information from a credit card or debit card.
CGI - Common Gateway Interface. This mechanism is used by HTTP servers (web servers) to pass parameters to executable scripts in order to generate responses dynamically.
Challenge-Handshake Authentication Protocol (CHAP) - The Challenge-Handshake Authentication Protocol uses a challenge/response authentication mechanism where the response varies every challenge to prevent replay attacks.
Cipher - A cryptographic algorithm for encryption and decryption.
Ciphertext - Ciphertext is the encrypted form of the message being sent.
Circuit Switched Network - A circuit switched network is where a single continuous physical circuit connected two endpoints where the route was immutable once set up.
Client - A system entity that requests and uses a service provided by another system entity, called a "server." In some cases, the server may itself be a client of some other server.
Collision - A collision occurs when multiple systems transmit simultaneously on the same wire.
Cookie - Data exchanged between an HTTP server and a browser (a client of the server) to store state information on the client side and retrieve it later for server use. An HTTP server, when sending data to a client, may send along a cookie, which the client retains after the HTTP connection closes. A server can use this mechanism to maintain persistent client-side state information for HTTP-based applications, retrieving the state information in later connections
Cookies - Small text files stored by a website on a computer to track information about a user's browsing behavior on a specific site.
Crimeware - Malware designed to automate cyber crime, specifically identity theft, to access a computer user's online accounts.
Cron - Cron is a Unix application that runs jobs for users and administrators at scheduled times of the day.
Cryptanalysis - The mathematical science that deals with analysis of a cryptographic system in order to gain knowledge needed to break or circumvent the protection that the system is designed to provide. In other words, convert the cipher text to plain text without knowing the key.
Cyber squatting - The act of registering a popular domain name with the intent of selling it to its rightful owner.
Cyber warfare - The practice of using computers and the Internet in conducting warfare in cyberspace.
Cyberbullying - Harassing, embarrassing, or threatening a person via the Internet, email and cellphone communication.