Glossary S & T

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• Script:

  It is a sequence of instructions that is interpreted or carried out by another program rather than by the computer's microprocessor (a complied program).

  Sector:

  Is a division of a disk's storage medium. It is the wedge shaped segment of a circular track, typically holding 512 bytes of data (1 byte= 8 bits).

  Services:

  Are specialized programs that perform functions that support other programs.
  They operate at a very low level and are run by the computer operating system.
  They interact directly with the hardware.

  Spam:

  A term referring to unwanted commercial e-mail, the equivalent to junk mail delivered to a mail box.
  A person or e-mail address that receives many unwanted messages.

  Spyware:

  Software that tracks user behavior without their knowledge.
  It can enter a system as a virus or bundled with a legitimate program.
  It is placed on your system without your knowledge.

  Stateful Firewall:

  Is a firewall that keeps track of the state of the network connections (to the Internet) traveling across it. The firewall is programmed to distinguish packets for different type of connections (TCP, UDP, FTP, etc.). Only packets matching a known connection state will be allowed, others will be rejected.

  This type of firewall holds in memory significant attributes of each connection. Such as IP addresses, ports used and packet sequence numbers. They are stored in what is known as a state table.

  The stateful firewall depends on the 3 way handshake of the TCP protocol.

  - The client sends a SYN bit in its header.
  - If the service is available it replies with a SYN bit and a ACK bit.
  - The client again responds with only an ACK bit.
  - The connection then enters the ESTABLISHED state.

  Stateless Firewall:

  Is a firewall that treats each network packet in isolation. This type of firewall has no way of knowing if a packet;

  - is part of an existing connection.
  - is trying to establish a new connection.
  - is a rogue packet.

  Modern firewall's are connection - aware (state - aware), giving network administrators finer control of network traffic.

  TCP (Transmission Control Protocol):

  It enables two computers (hosts) to establish a connection and exchange streams of data. TCP guarantees delivery of data and that the data packets will be delivered in the same order in which they were sent.

  TCP/IP (Transmission Control Protocol / Internet Protocol):

  Is a language governing communication among computers on the Internet.
  It is two separate protocols used together.
  The IP part, dictates how packets of information are sent over the Internet (networks), and has the addressing method.
  TCP ensures the data reliability over the network. It checks for errors, making requests for re-transmission if errors are found.
  TCP ensures the data packets of a message are received in the correct order at the destination.

  Thread:

  An entity of executable code within a process, that is scheduled for execution.
  It includes;

  - the contents of the microprocessor registers,
  - a segregated memory area,
  - runtime libraries & dlls, and
  - a unique identifier (thread ID).

  Trojan Horse:

  It often takes on the form of an e-mail attachment.
  It's a small program that hides on your computer, performing such tasks from data destruction to information retrieval.
  The Trojan Horse is typically received via an e-mail with the code imbedded in an attachment. The attachment installs the Trojan Horse, locks up the operating system, requiring a system re-boot. After the re-boot the Trojan Horse runs, performing its intended action.
  It can give a remote user control over an infected computer, accessing passwords, credit card numbers, etc.

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