virus- this term is usually heard in biology or even in computers. unlike in biological matters, computer virus are man-made.A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.once the virus infects the computer , it can spread throughout and may damage files and system software, including the operating system. http://www.webopedia.com/TERM/V/virus.htmlrm-

worms -is a program that copies itself repeatedly, for example in memory or on a network, using up resources and possibly shutting down the computer or network. Worms are able to rapidly replicate by hijacking an infected system’s resources to seek out and exploit other systems with a particular vulnerability. This predisposition to spread itself as quickly and widely as possible can often overload system memory as well as bring down entire corporate networks as traffic is consumed by the worms procedures. Many worms come in the form of email file attachments, or as hidden additions to actual email messages, which trigger the execution of infectious code. The Melissa virus are examples of worms that exploited the macro feature within Microsoft Office documents. http://articles.winferno.com/antivirus/computer-worms/\

trojan horse- (named after the Greek myth) is a program that hides within or looks like a legitimate program. a certain condition usually triggers the Trojan horse.Trojan horses do not replicate themselves but they can be just as destructive. One of the most insidious types of Trojan horse is a program that claims to rid your computer of viruses but instead introduces viruses onto your computer.

1) The essential data that is being carried within a packet or other transmission unit. The payload does not include the "overhead" data required to get the packet to its destination. Note that what constitutes the payload may depend on the point-of-view. To a communications layer that needs some of the overhead data to do its job, the payload is sometimes considered to include the part of the overhead data that this layer handles. However, in more general usage, the payload is the bits that get delivered to the end user at the destination.


2) The eventual effect of a software virus that has been delivered to a user's computer.

Payload in computing (sometimes referred to as the actual or body data) is the cargo of a data transmission. It is the part of the transmitted data which is the fundamental purpose of the transmission, to the exclusion of information sent with it (such as headers or metadata, sometimes referred to as overhead data) solely to facilitate delivery.[1][2]
In the analysis of malicious software such as worms, viruses and Trojans, it refers to the software's harmful results. Examples of payloads include data destruction, messages with insulting text or spurious e-mail messages sent to a large number of people.

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer or network resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted efforts of a person, or multiple people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely. Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root name servers. The term is generally used relating to computer networks, but is not limited to this field; for example, it is also used in reference to CPU resource management.

One common method of attack involves saturating the target machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. Such attacks usually lead to a server overload. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.

Denial-of-service attacks are considered violations of the IAB's Internet proper use policy, and also violate the acceptable use policies of virtually all Internet services providers. They also commonly constitute violations of the laws of individual nations.

When the DoS Attacker sends many packets of information and requests to a single network adapter, each computer in the network would experience effects from the DoS attack

Spoofing -The word "spoof" means to hoax, trick, or deceive. Therefore, in the IT world, spoofing refers tricking or deceiving computer systems or other computer users. This is typically done by hiding one's identity or faking the identity of another user on the Internet.

Spoofing can take place on the Internet in several different ways. One common method is through e-mail. E-mail spoofing involves sending messages from a bogus e-mail address or faking the e-mail address of another user. Fortunately, most e-mail servers have security features that prevent unauthorized users from sending messages. However, spammers often send spam messages from their own SMTP, which allows them to use fake e-mail addresses. Therefore, it is possible to receive e-mail from an address that is not the actual address of the person sending the message.

 back door- is a means of access to a computer program that bypasses security mechanisms. A programmer may sometimes install a back door so that the program can be accessed for troubleshooting or other purposes. However, attackers often use back doors that they detect or install themselves, as part of an exploit. In some cases, a worm is designed to take advantage of a back door created by an earlier attack. For example, Nimdagained entrance through a back door left by Code Red

A honey pot is a computer system on the Internet that is expressly set up to attract and "trap" people who attempt to penetrate other people's computer systems. (This includes the hacker, cracker, and script kiddy.) To set up a honey pot, it is recommended that you:

·         Install the operating system without patches installed and using typical defaults and options

·         Make sure that there is no data on the system that cannot safely be destroyed

·         Add the application that is designed to record the activities of the invader

Maintaining a honey pot is said to require a considerable amount of attention and may offer as its highest value nothing more than a learning experience (that is, you may not catch any hackers).

botnet (also known as a zombie army) is a number of Internet computers that, although their owners are unaware of it, have been set up to forward transmissions (including spam or viruses) to other computers on the Internet. Any such computer is referred to as a zombie - in effect, a computer "robot" or "bot" that serves the wishes of some master spam or virus originator. Most computers compromised in this way are home-based. According to a report from Russian-based Kaspersky Labs, botnets -- not spam, viruses, or worms -- currently pose the biggest threat to the Internet. A report from Symantec came to a similar conclusion.

firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass.

A firewall is a set of related programs, located at a network gateway server, that protects the resources of a private network from users from other networks. (The term also implies the security policy that is used with the programs.) An enterprise with an intranet that allows its workers access to the wider Internet installs a firewall to prevent outsiders from accessing its own private data resources and for controlling what outside resources its own users have access to.