T1, T3 - A digital circuit using TDM (Time-Division Multiplexing).
Tamper - To deliberately alter a system's logic, data, or control information to cause the system to perform unauthorized functions or services.
TCP Fingerprinting - TCP fingerprinting is the user of odd packet header combinations to determine a remote operating system.
TCP Full Open Scan - TCP Full Open scans check each port by performing a full three-way handshake on each port to determine if it was open.
TCP Half Open Scan - TCP Half Open scans work by performing the first half of a three-way handshake to determine if a port is open.
TCP Wrapper - A software package which can be used to restrict access to certain network services based on the source of the connection; a simple tool to monitor and control incoming network traffic.
TCP/IP - A synonym for "Internet Protocol Suite;" in which the Transmission Control Protocol and the Internet Protocol are important parts. TCP/IP is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network (either an Intranet or an Extranet).
Tiny Fragment Attack - With many IP implementations it is possible to impose an unusually small fragment size on outgoing packets. If the fragment size is made small enough to force some of a TCP packet's TCP header fields into the second fragment, filter rules that specify patterns for those fields will not match. If the filtering implementation does not enforce a minimum fragment size, a disallowed packet might be passed because it didn't hit a match in the filter. STD 5, RFC 791 states: Every Internet module must be able to forward a datagram of 68 octets without further fragmentation. This is because an Internet header may be up to 60 octets, and the minimum fragment is 8 octets.
Token Ring - A token ring network is a local area network in which all computers are connected in a ring or star topology and a binary digit or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.
Token-Based Access Control - Token based access control associates a list of objects and their privileges with each user. (The opposite of list based.)
Token-Based Devices - A token-based device is triggered by the time of day, so every minute the password changes, requiring the user to have the token with them when they log in.
Topology - The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network. Note 1: Two networks have the same topology if the connection configuration is the same, although the networks may differ in physical interconnections, distances between nodes, transmission rates, and/or signal types. Note 2: The common types of network topology are illustrated
Traceroute (tracert.exe) - Traceroute is a tool the maps the route a packet takes from the local machine to a remote destination.
Transmission Control Protocol (TCP) - A set of rules (protocol) used along with the Internet Protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called packets) that a message is divided into for efficient routing through the Internet. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.
Transport Layer Security (TLS) - A protocol that ensures privacy between communicating applications and their users on the Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message. TLS is the successor to the Secure Sockets Layer.
Triple DES - A block cipher, based on DES, that transforms each 64-bit plaintext block by applying the Data Encryption Algorithm three successive times, using either two or three different keys, for an effective key length of 112 or 168 bits.
Trojan - A malicious program that appears to perform or actually performs a desired task for a user while performing a harmful task without the user's knowledge or consent.
Tunnel - A communication channel created in a computer network by encapsulating a communication protocol's data packets in (on top of) a second protocol that normally would be carried above, or at the same layer as, the first one. Most often, a tunnel is a logical point-to-point link - i.e., an OSI layer 2 connection - created by encapsulating the layer 2 protocol in a transport protocol (such as TCP), in a network or inter-network layer protocol (such as IP), or in another link layer protocol. Tunneling can move data between computers that use a protocol not supported by the network connecting them.
Typosquatting - A practice that relies on mistakes such as typographical errors made by web users when typing an URL into a web browser.