Blended threat
A blended threat is an attack which combines different characteristics specific to viruses, worms, Trojan Horses and other malicious code (malware). It exploits Internet or server vulnerabilities in order to transmit and spread itself. A ‘blended threat’ attacks using multiple methods and techniques.
Blended threats are initiated with the intent to cause real harm, for example launching a Denial of Service (DoS) on a target computer, defacing Web servers or planting a Trojan Horse program for later execution. A blended threat spreads using multiple methods. It scans for vulnerabilities to compromise a system, such as embedding code in HTML files on a server, infecting visitors through a compromised Web site or sending unauthorized e-mail with worm attachments from compromised servers. Blended threats attack from multiple points. They inject malicious code into the .exe files on a system, raise the privilege level of the guest account, make numerous registry changes and can even spread without human intervention. Blended threats also take advantage of known vulnerabilities producing buffer overflows, HTTP input validation vulnerabilities and known default passwords to gain unauthorized administrative access.
Effective protection from blended threats requires the use of a firewall, regular patch updating and the running of software specially designed to detect malware.

Computer Virus
The term computer virus derives from its biological counterpart. Both share the same main characteristics. Computer viruses were first investigated as part of academic research on artificial intelligence. Computer networks are mainly rendered susceptible to virus infections by the monoculture of the software environments being used.
As in the biological context, where the genetic diversity of a population decreases the chances of total destruction by viral infection or diseases, the diversity of software systems in a network environment limits the destructive potential of computer viruses. In computer science, a virus is a (usually malicious) program able to add or send a replica of itself to infect other programs or operating systems. The infection can spread itself to other computers through storage devices or computer networks. Most viruses consist of a finder (identifying new and uninfected files) and a replicator (which opens the file identified by the finder, performs the “infection” and then returns to the finder so that it can find new files for the replicator to infect). Some viruses can cause global havoc within minutes or hours, but many are benign or just annoying. There are several types of computer viruses:
- Traditional viruses (pieces of code self-replicating on other programs and documents),
- E-mail viruses (programs or documents attached to an e-mail message which, when opened, spreads and generates e-mail messages containing themselves as an attachment)
- Worms
- Polymorphic viruses (combination of encryption and self-modifying code created to hide the virus and avoid pattern recognition from antivirus software). Polymorphic viruses imitate pseudo-Darwinian evolution; the virus mutates, creating endless variations of itself, and “survival of the fittest” allows only the stealthiest to reproduce and mutate further.

Worm
A worm is a computer program capable of self-replicating across network connections using available resources of a system or a network. In contrast to a virus, a worm is self-contained and does not need to attach itself to another program in order to propagate. A worm can be designed to perform a range of different tasks or even carry other executable tasks as payloads (e.g. backdoors or viruses).

Trojan Horse
A Trojan Horse is a piece of software disguised as a useful task or utility. It contains hidden malicious code programmed to get control over the system and to allow the unauthorized collection, falsification or destruction of data. Trojan Horses are similar to backdoors, but unlike viruses and worms Trojan Horses do not replicate themselves.

Distributed Attack
A hacker/cracker begins a distributed Denial of Service attack (DDoS) by taking control of one computer system. This system becomes a “DDoS master”. From this master system the intruder takes control of a multitude of other systems, loading specific cracking tools on to them. A single command can cause all controlled machines to launch a flood attack against a specified target causing a DoS and eventually forcing the targeted system to shut down.

Denial of Service
An incident in which a single user or a network loses access to resources, network services or all network connectivity that is normally granted is called Denial of Service (DoS). A Denial of Service attack can cause a website to cease operating and can destroy programs and files in a computer system.
The most common forms of Denial of Service are:
- Buffer Overflow Attacks - sending more information to a program or a system than its data buffer can handle
- Teardrop Attack - exploits the way Internet Protocol (IP) divides over-large packets by placing confusing offset values in the second or subsequent fragments so that the whole packet cannot be reassembled. This causes the entire system to crash
- Smurf Attack - an “echo my message back to me” a.k.a. Ping message is broadcast to a number of hosts within a local network, replacing the sender's address with the address of the site to receive the DoS. This action is also called Spoofing
- Viruses - viruses self-reproduce across the network causing DoS attacks on victims not specifically targeted.

Backdoor
A piece of code attached to a program (often known only to the programmer) allowing secret and illegal access to a program, a service or to entire computer systems. A backdoor, also called trapdoor, is a potential security risk.

Payload
A payload is an action carried out by certain viruses in an infected computer system in addition to spreading and reproducing themselves. Not all viruses carry payloads. Payloads range from harmless text, image or sound messages displayed on the monitor right through to the extremely destructive kind of actions that delete the entire hard disk. This terminal shows a selection of visual payloads taken directly from infected computers.

Source code / programming language / virus
Source code is a communication level between a user and a computer, between human and machine. The computer only understands instructions in form of binary code. In order to write a program without having to use binary code (series of 0 and 1) the coder uses a text, a sort of algebra, which gives the machine instructions in a specific computer language such as Java, C, C++, Visual Basics or Assembler. To be computer executable, this source code finally has to be translated back into binary code, a task executed by a specific program, a compiler.

The comprehensibility of source codes is enhanced by the addition of useful comments and explanations. In this way, programmers enable other users working with software to understand how a specific program functions. If a user only receives the executable code he cannot modify it, even if that were permitted. Therefore in order to increase the quality or the usefulness of specific software a user needs the source code.

Source code is a product of human intellect, answering the needs of contemporary culture for many different software applications. Source code does not only fulfil a distinct function but also has its own aesthetic and follows its own method. Therefore source code is a new form of language - programming “language” has its own formal logic and form, just like spoken and written human language.

Computer program
Computers have two main components: the hardware (physical parts and components) and the software (a set of programs that tell the hardware what to do). A program is a detailed plan or procedure meant to perform a specific task when executed; it contains a list of variables (numerical data, text, graphic images) and a list of instructions or statements which tell the computer what to do with the variables. Every computer program is written in a specific programming language.

Operating system
Every computer has a software platform called an operating system, on which all the other programs, called application programs, can run.
An operating system performs basic tasks like receiving input from the keyboard, sending output to the monitor, controlling peripheral devices and managing information storage on the hard disk. The operating system coordinates the execution of different simultaneous tasks and manages hardware resource-sharing in such a way that all the tasks are completed without interfering with each another.

Binary code
The base 2 (binary) number system requires only two symbols - “0" and "1”. In computer technology, this system represents data with two states - “on-off”, “open-closed”, “go-no go”. Binary code is a compact and reliable coding system which is used by computers to convert all information like letters, numbers, punctuation marks and control characters into standardized digital format. Binary code allows a computer to efficiently process and store data and communicate with other computers or entire networks. Computers use a binary code that is arranged in groups of eight digits, or bits; each such group forms a byte.