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Malware: viruses, worms, trojans and spyware
By far the most common type of computer crime involves malware.
Malware (malicious software) is software created to damage or alter the computer data or its operations. Malware includes computer viruses, worms, trojan horses, most rootkits, spyware, dishonest adware, crimeware, and other malicious and unwanted software, including true viruses.
Viruses are self-replicating programs that spread by inserting copies of themselves into other executable code or documents. Thus, a computer virus behaves in a way similar to a biological
itself to everyone in an email address book.
A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive.
The term "computer virus" is sometimes used as a catch-all phrase to include all types of malware. Viruses are sometimes confused with computer worms and Trojan horses, which are technically different.
between a virus and a worm is that a worm does not create multiple copies of itself on one system: it propagates through computer networks. A worm can exploit security vulnerabilities to spread itself to other computers without needing to be transferred as part of a host. After the comparison between computer viruses and biological viruses, the obvious comparison here is to a bacterium. Many people conflate the terms "virus" and "worm", using them both to describe any self-propagating program. It is possible for a program to have the blunt characteristics of both a worm and a virus.
to collect stored data. They don't copy themselves or reproduce by infecting other files.
A Trojan horse is a program designed as to seem to being or be doing one thing, such as legitimate software, but actually being or doing another. They are not necessarily malicious programs but can be. A Trojan horse can be used to set up a back door in a computer system so that the intruder can return later and gain access. Viruses that fool a user into downloading and/or executing them by pretending to be useful applications are also sometimes called Trojan horses. (The name refers to the horse from the Trojan War, with conceptually similar function of deceiving defenders into bringing an intruder inside.) Worms and Trojans, like viruses, may cause harm to either a computer system's hosted data, functional performance, or networking throughput, when they are executed. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious.
system details or, in its most dangerous form, passwords and login information for critical applications such as online banking. Many spyware programs are more annoying than dangerous, serving up pop-up ads or gathering e-mail addresses for use in spam campaigns. Even those programs, however, can cost you valuable time and computing resources. Often, spyware comes along with a free software application, such as a game or a supposed productivity booster.
Adware is similar to spyware and malware, in that it resides on a computer without the user's knowledge; adware specifically refers to programs that display pop-up advertisements. The subject matter of the ads is often based on surfing habits, but may also be tied to a specific advertiser.
While cookies aren't really malware, they can be used in similar ways. Cookies are small data files used by Web sites to store information on your computer. For example, a shopping site may want to identify items you've looked at, but not purchased, or store data on current purchases until you head for the checkout. A less scrupulous site, however, may decide to look through your cookies for personal information, such as recent sites you have visited.
procedures, allowing a cracker to access information on another computer.
Key loggers - programs that record keystrokes made by a user, allowing crackers to discover passwords, login codes and other confidential information.
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