Viruses, worms, spyware and adware
The term "computer virus" is commonly used to refer to any piece of malicious software whose purpose is at best to make some type of personal statement by the author (e.g., "I did it!") and at worst to destroy computer-based information, to shut down networks by creating enormous amounts of network traffic and to cost organizations potentially millions of dollars in clean-up costs.
However, while viruses can do all of the above things, this definition is not technically correct. Malicious software is considered a virus only when it has the following three characteristics:
- it can hunt for target systems, software and/or documents to infect,
- it can add or send a replica of itself to ("infect") its chosen targets, and
- it can perform any or all of the undesirable functions described in the first paragraph.
In this sense, a computer virus truly mimics the operation of a biological counterpart which hunts for cells it can infect, alters the genetic makeup of a target cell to produce more viral replicas, and potentially produces disease.
Other types of malicious software include:
- Worms are pieces of code added to a program or document that, when opened, spread by using the infected computer's network connection to search for and exploit unaddressed security vulnerabilities in other computers' operating systems, network software, Web server software, database software, and applications.
- Spyware and adware are programs that can be secretly installed on your computer when you access the websites on the Internet that distribute them. The stated intent of these programs is often to determine your interests so that Internet sites can tailor their advertising to those interests. This can involves capturing the names (or URLs) of the websites you visit and storing that information either on an Internet-based computer or on your own computer in small files known as "cookies," or by installing software. Spyware and adware have been known to intentionally or unintentionally degrade the performance of your system, uncover confidential data on your system, capture passwords, and destroy data.
