What Is the Difference: Viruses, Worms, Trojans, and Bots?

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What Is the Difference: Viruses, Worms, Trojans, and Bots?

Viruses, worms, Trojans, and bots are all part of a class of software called malware. Malware or malicious code (malcode) is short for malicious software. It is code or software that is specifically designed to damage, disrupt, steal, or in general inflict some other “bad” or illegitimate action on data, hosts, or networks.

There are many different classes of malware that have varying ways of infecting systems and propagating themselves. Malware can infect systems by being bundled with other programs or attached as macros to files. Others are installed by exploiting a known vulnerability in an operating system (OS), network device, or other software, such as a hole in a browser that only requires users to visit a website to infect their computers. The vast majority, however, are installed by some action from a user, such as clicking an email attachment or downloading a file from the Internet.

Some of the more commonly known types of malware are viruses, worms, Trojans, bots, backdoors, spyware, and adware. Damage from malware varies from causing minor irritation (such as browser popup ads), to stealing confidential information or money, destroying data, and compromising and/or entirely disabling systems and networks.

Malware cannot damage the physical hardware of systems and network equipment, but it can damage the data and software residing on the equipment. Malware should also not be confused with defective software, which is intended for legitimate purposes but has errors or bugs.


Classes of Malicious Software
Two of the most common types of malware are viruses and worms. These types of programs are able to self-replicate and can spread copies of themselves, which might even be modified copies. To be classified as a virus or worm, malware must have the ability to propagate. The difference is that a worm operates more or less independently of other files, whereas a virus depends on a host program to spread itself. These and other classes of malicious software are described below.

A computer virus is a type of malware that propagates by inserting a copy of itself into and becoming part of another program. It spreads from one computer to another, leaving infections as it travels. Viruses can range in severity from causing mildly annoying effects to damaging data or software and causing denial-of-service (DoS) conditions. Almost all viruses are attached to an executable file, which means the virus may exist on a system but will not be active or able to spread until a user runs or opens the malicious host file or program. When the host code is executed, the viral code is executed as well. Normally, the host program keeps functioning after it is infected by the virus. However, some viruses overwrite other programs with copies of themselves, which destroys the host program altogether. Viruses spread when the software or document they are attached to is transferred from one computer to another using the network, a disk, file sharing, or infected email attachments.

Computer worms are similar to viruses in that they replicate functional copies of themselves and can cause the same type of damage. In contrast to viruses, which require the spreading of an infected host file, worms are standalone software and do not require a host program or human help to propagate. To spread, worms either exploit a vulnerability on the target system or use some kind of social engineering to trick users into executing them. A worm enters a computer through a vulnerability in the system and takes advantage of file-transport or information-transport features on the system, allowing it to travel unaided.

A Trojan is another type of malware named after the wooden horse the Greeks used to infiltrate Troy. It is a harmful piece of software that looks legitimate. Users are typically tricked into loading and executing it on their systems. After it is activated, it can achieve any number of attacks on the host, from irritating the user (popping up windows or changing desktops) to damaging the host (deleting files, stealing data, or activating and spreading other malware, such as viruses). Trojans are also known to create back doors to give malicious users access to the system.

Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate. Trojans must spread through user interaction such as opening an e-mail attachment or downloading and running a file from the Internet.

“Bot” is derived from the word “robot” and is an automated process that interacts with other network services. Bots often automate tasks and provide information or services that would otherwise be conducted by a human being. A typical use of bots is to gather information (such as web crawlers), or interact automatically with instant messaging (IM), Internet Relay Chat (IRC), or other web interfaces. They may also be used to interact dynamically with websites.

Bots can be used for either good or malicious intent. A malicious bot is self-propagating malware designed to infect a host and connect back to a central server or servers that act as a command and control (C&C) center for an entire network of compromised devices, or “botnet.” With a botnet, attackers can launch broad-based, “remote-control,” flood-type attacks against their target(s). In addition to the worm-like ability to self-propagate, bots can include the ability to log keystrokes, gather passwords, capture and analyze packets, gather financial information, launch DoS attacks, relay spam, and open back doors on the infected host. Bots have all the advantages of worms, but are generally much more versatile in their infection vector, and are often modified within hours of publication of a new exploit. They have been known to exploit back doors opened by worms and viruses, which allows them to access networks that have good perimeter control. Bots rarely announce their presence with high scan rates, which damage network infrastructure; instead they infect networks in a way that escapes immediate notice.

Best Practices

  • Install reputable Anti-Virus and Anti-Malware programs.
  • Keep your Anti-Virus and Anti-Malware programs up to date.
  • Regularly scan your computer with your Antiv-Virus/Anti-Malware programs.
  • Regularly update your Operating System.
  • Secure your home wifi network.
  • Avoiding visiting unknown sites and clicking on unknown links.
  • Do not display personal information on your online accounts.
  • Do not use open wifi.
  • Backup your files.
  • Use unique strong passwords ideally with password manager.





Computer keyboard shortcut commands

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Computer keyboard shortcut keys

Shortcut keys help provide an easier and usually quicker method of navigating and executing commands in computer software programs. Shortcut keys are commonly accessed by using the Alt key (on IBM compatible computers),Command key (on Apple computers), Ctrl key, or Shift key in conjunction with another key. The de facto standard for listing a shortcut is listing the modifier key, a plus symbol, and another key. In other words, “Ctrl+S” is telling you to press and hold the Ctrl key, and then press the S key too.

You can also find the shortcut keys to their most popular program by looking for underlined letters in their menus. For example, the image to the right has an underline on the “F” in File, which means you can press the Alt key and then the “F” key to access the File menu.

File photo

Some programs require the user to press and hold Alt to see the underlined characters. In the same image above, you can see that some of the common features, such as Open (Ctrl+O) and Save (Ctrl+S), have shortcut keys assigned to them. As you begin to memorize shortcut keys, you’ll notice that many applications share the same shortcut keys. We have a list of the most commonly shared ones in the basic PC shortcut keys section.

Tip: Users outside the United States or who have a foreign copy of Microsoft Windows or a Microsoft application may not be able to use all of the below shortcut keys.

Basic PC Shortcut Keys

Below is a list of some of the most commonly used basic shortcut keys that work with almost all IBM compatible computers and software programs. It is highly recommended that all users keep a good reference of these shortcut keys or try to memorize them. Doing so will dramatically increase your productivity.

Tip: Besides the special character shortcuts listed here, some special characters are also located on the number keys (below the F1 – F12 keys). You can enter these special characters by pressing the Shift key and the number key that has the special character listed on it.

Shortcut Keys Description Shortcut Keys Description
Alt + F File menu options in current program Shift + Ins Copy selected item
Alt + E Edit options in current program Ctrl + V Paste
Alt+ Tab Switch between open programs Shift + Ins Paste
F1 Universal Help in almost every Windows program Ctrl + K Insert hyperlink for selected text
F2 Rename a selected file Ctrl + P Print the current page or document
F5 Refresh the current program window Home Goes to beginning of current line
Ctrl + N Create a new, blank document in some software programs Ctrl + Home Goes to beginning of document
Ctrl + O Open a file in current software program Shift + End Highlights from current position to end of line
Ctrl + A Select all text Ctrl + Left Arrow Moves one word to the left at a time
Ctrl + B Change selected text to be Bold Ctrl + Right Arrow Moves one word to the right at a time
Ctrl + I Change selected text to be in Italics Ctrl + Esc Opens the START menu
Ctrl + U Change selected text to be Underlined Ctrl + Shift + Esc Opens Windows Task Manager
Ctrl + F Open find window for current document or window Alt + F4 Close the currently active program
Ctrl + S Save current document file Alt + Enter Open the Properties for the selected item (file, folder, shortcut, etc.)
Ctrl + X Cut selected item End Goes to end of current line
Shift + Del Cut selected item Ctrl + End Goes to end of document
Ctrl + C Copy selected item