From Wikipedia, the free encyclopaedia
"Malware, short for malicious software, is software designed to infiltrate a computer system without the owner's informed consent. The expression is a general term used by computer professionals to mean a variety of forms of hostile, intrusive, or annoying software or program code. The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware, including true viruses. Software is considered to be malware based on the perceived intent of the creator rather than any particular features. Malware includes computer viruses, worms, trojan horses, spyware, dishonest adware, crimeware, most rootkits, and other malicious and unwanted software. Malware is not the same as defective software, that is a software that has a legitimate purpose but contains harmful bugs. Preliminary results from Symantec published in 2008 suggested that "the release rate of malicious code and other unwanted programs may be exceeding that of legitimate software applications." According to FSecure, "As much malware was produced in 2007 as in the previous 20 years altogether." Malware's most common pathway from criminals to users is through the Internet: primarily by e-mail and the World Wide Web."

Trojan horses, rootkits, and backdoors

Regardless of the repository model that is used, the data has to be stored on some data storage medium somewhere.

Trojan Horses

For a malicious program to accomplish its goals, it must be able to run without being shut down, or deleted by the user or administrator of the computer system on which it is running. Concealment can also help get the malware installed in the first place. When a malicious program is disguised as something innocuous or desirable, users may be tempted to install it without knowing what it does. This is the technique of the Trojan horse or trojan.

In broad terms, a Trojan horse is any program that invites the user to run it, concealing a harmful or malicious payload. The payload may take effect immediately and can lead to many undesirable effects, such as deleting the user's files or further installing malicious or undesirable software. Trojan horses known as droppers are used to start off a worm outbreak, by injecting the worm into users' local networks.

One of the most common ways that spyware is distributed is as a Trojan horse, bundled with a piece of desirable software that the user downloads from the Internet. When the user installs the software, the spyware is installed alongside. Spyware authors who attempt to act in a legal fashion may include an end-user license agreement that states the behaviour of the spyware in loose terms, which the users are unlikely to read or understand.


Once a malicious program is installed on a system, it is essential that it stays concealed, to avoid detection and disinfection. The same is true when a human attacker breaks into a computer directly. Techniques known as rootkits allow this concealment, by modifying the host's operating system so that the malware is hidden from the user. Rootkits can prevent a malicious process from being visible in the system's list of processes, or keep its files from being read. Originally, a rootkit was a set of tools installed by a human attacker on a Unix system, allowing the attacker to gain administrator (root) access. Today, the term is used more generally for concealment routines in a malicious program.

Some malicious programs contain routines to defend against removal, not merely to hide themselves, but to repel attempts to remove them. An early example of this behaviour is recorded in the Jargon File tale of a pair of programs infesting a Xerox CP-V time sharing system:

Each ghost-job would detect the fact that the other had been killed, and would start a new copy of the recently slain program within a few milliseconds. The only way to kill both ghosts was to kill them simultaneously (very difficult) or to deliberately crash the system.

Similar techniques are used by some modern malware, wherein the malware starts a number of processes that monitor and restore one another as needed. In the event a user running Microsoft Windows is infected with such malware, if they wish to manually stop it, they could use Task Manager's 'processes' tab to find the main process (the one that spawned the "resurrector process(es)"), and use the 'end process tree' function, which would kill not only the main process, but the "resurrector(s)" as well, since they were started by the main process. Some malware programs use other techniques, such as naming the infected file similar to a legitimate or trust-able file (expl0rer.exe VS explorer.exe).


A backdoor is a method of bypassing normal authentication procedures. Once a system has been compromised (by one of the above methods, or in some other way), one or more backdoors may be installed in order to allow easier access in the future. Backdoors may also be installed prior to malicious software, to allow attackers entry. The idea has often been suggested that computer manufacturers preinstall backdoors on their systems to provide technical support for customers, but this has never been reliably verified. Crackers typically use backdoors to secure remote access to a computer, while attempting to remain hidden from casual inspection. To install backdoors crackers may use Trojan horses, worms, or other methods.

Spyware, botnets, keystroke loggers, and diallers

During the 1980s and 1990s, it was usually taken for granted that malicious programs were created as a form of vandalism or prank. More recently, the greater share of malware programs have been written with a financial or profit motive in mind. This can be taken as the malware authors' choice to monetize their control over infected systems: to turn that control into a source of revenue.

Spyware programs are commercially produced for the purpose of gathering information about computer users, showing them pop-up ads, or altering web-browser behaviour for the financial benefit of the spyware creator. For instance, some spyware programs redirect search engine results to paid advertisements. Others, often called "stealware" by the media, overwrite affiliate marketing codes so that revenue is redirected to the spyware creator rather than the intended recipient.

Spyware programs are sometimes installed as Trojan horses of one sort or another. They differ in that their creators present themselves openly as businesses, for instance by selling advertising space on the pop-ups created by the malware. Most such programs present the user with an end-user license agreement that purportedly protects the creator from prosecution under computer contaminant laws. However, spyware EULAs have not yet been upheld in court.

Another way that financially motivated malware creators can profit from their infections is to directly use the infected computers to do work for the creator. The infected computers are used as proxies to send out spam messages. A computer left in this state is often known as a zombie computer. The advantage to spammers of using infected computers is they provide anonymity, protecting the spammer from prosecution. Spammers have also used infected PCs to target antispam organizations with distributed denial-of-service attacks.

In order to coordinate the activity of many infected computers, attackers have used coordinating systems known as botnets. In a botnet, the malware or malbot logs in to an Internet Relay Chat channel or other chat system. The attacker can then give instructions to all the infected systems simultaneously. Botnets can also be used to push upgraded malware to the infected systems, keeping them resistant to antivirus software or other security measures.

It is possible for a malware creator to profit by stealing sensitive information from a victim. Some malware programs install a key logger, which intercepts the user's keystrokes when entering a password, credit card number, or other information that may be exploited. This is then transmitted to the malware creator automatically, enabling credit card fraud and other theft. Similarly, malware may copy the CD key or password for online games, allowing the creator to steal accounts or virtual items.

Another way of stealing money from the infected PC owner is to take control of a dial-up modem and dial an expensive toll call. Dialler (or porn dialler) software dials up a premium-rate telephone number such as a U.S. "900 number" and leave the line open, charging the toll to the infected user.

Datastealing malware

Data-stealing malware is a web threat that divests victims of personal and proprietary information with the intent of monetizing stolen data through direct use or underground distribution. Content security threats that fall under this umbrella include keyloggers, screen scrapers, spyware, adware, backdoors, and bots. The term does not refer to activities such as spam, phishing, DNS poisoning, SEO abuse, etc. However, when these threats result in file download or direct installation, as most hybrid attacks do, files that act as agents to proxy information will fall into the data-stealing malware category.

CHAPtech can help

If you suspect you have been a victim of Malware, contact Chaptech immediately for advice on how to remove the offending software.

The best defence for avoiding Malware is to:

  • Have effective SPAM filtering in place
  • Have up-to-date Antivirus protection
  • Do not allow 3rd party access to your system without ensuring they have the appropriate protection in place
  • To ensure your staff are aware of the potential negative effects their Internet browsing habits can have on the operations of your business