What are pop-ups?

Pop-up ads are a form of online advertising on the World Wide Web intended to increase web traffic or capture email addresses. It works when certain web sites open a new web browser window to display advertisements. The pop-up window containing an advertisement is usually generated by JavaScript, but can be generated by other means as well.

A variation on the pop-up window is the pop-under advertisement. This opens a new browser window, behind the active window. Pop-unders interrupt the user less, but are not seen until the desired windows are closed, making it more difficult for the user to determine which Web site opened them.

Where you least expect it:

Other pop-ups appear to come from perfectly legitimate websites that have been hijacked to link to other websites, usually in the form of pop-unders (see below). Online dating services are most prevalent in this category Many of these so called "free" dating services are known to harvest email addresses and create false accounts for the purposes of increasing site traffic and boosting advertising revenue. Accounts created in this way usually only remain active for three to four weeks, before the hijack is discovered and the account deleted.

A different sort of pop-up ad can be sent via the Messenger service in Microsoft's Windows operating system. These pop-ups appear as Windows dialog boxes with a textual message inside, usually directing the user to a Web site. Claims have been made that this type of pop-up has been used to commit extortion. Threats of legal action against the company D Squared Solutions has caused them to stop using this technique.

In simpler terms, Spyware is a type of program that watches after what users do with their computer and then send this information to a hacker over the internet. Spyware can collect many different types of information about a user. More benign programs can attempt to track what types of websites a user visits and send this information to an advertisement agency. More malicious versions can try to record what a user types to try to intercept passwords or credit card numbers. Yet other versions simply launch pop-ups with advertisements.

The name 'worm' was taken from The Shockwave Rider, a science fiction novel published in 1975 by John Brunner. Researchers writing an early paper on experiments in distributed computing noted the similarities between their software and the program described by Brunner and adopted the name.

Although technically a Trojan, the Christmas Tree Worm was the first worm on a worldwide network, spreading across both IBM's own international network and BITNET in December 1987 - and bringing both to their knees.

The first worm on the Internet, and the first to attract wide attention, the Morris worm, was written by Robert Tappan Morris, who at the time was a graduate student at Cornell University. It was released on November 2, 1988, and quickly infected a great number of computers on the Internet at the time, and causing massive disruption. It propagated through a number of bugs in BSD Unix and its derivatives. Morris himself was convicted under the US Computer Crime and Abuse Act and received three years probation, 400 hours community service and a fine in excess of $10,000.

In addition to replication, a worm may be designed to do any number of things, such as delete files on a host system, encrypt files in a cryptoviral extortion attack, or send documents via e-mail. More recent worms may be multi-headed and carry other executables as a payload. However, even in the absence of such a payload, a worm can wreak havoc just with the network traffic generated by its reproduction. Mydoom, for example, caused a noticeable worldwide Internet slowdown at the peak of its spread.

A common "payload" is for a worm to install a "backdoor" in the infected computer, as was done by "Sobig" and "Mydoom." These zombie computers are used by spam senders for sending junk email or to cloak their website's address. Spammers are thought to fund the creation of such worms, and worm writers have been caught selling lists of IP addresses of infected machines. Others try to blackmail companies with threatened DoS (Denial of Service) attacks. The "backdoors" can also be exploited by other worms, such as "Doomjuice", which spreads using the backdoor opened by Mydoom.

Often the term is shortened to simply Trojan, even though this turns the adjective into a noun, reversing the myth (Greeks were gaining malicious access, not Trojans).

There are two common types of Trojan horses. One, is otherwise useful software that has been corrupted by a cracker inserting malicious code that executes while the program is used. Examples include various implementations of weather alerting programs, computer clock setting software, and peer to peer file sharing utilities. The other type is a standalone program that masquerades as something else, like a game or image file, in order to trick the user into some misdirected complicity that is needed to carry out the program's objectives.

Trojan horse programs cannot operate autonomously, in contrast to some other types of malware, like viruses or worms. Just as the Greeks needed the Trojans to bring the horse inside for their plan to work, Trojan horse programs depend on actions by the intended victims. As such, if Trojans replicate and even distribute themselves, each new victim must run the program/Trojan. Therefore their virulence is of a different nature, depending on successful implementation of social engineering concepts rather than flaws in a computer system's security design or configuration.

In practice, Trojan Horses in the wild often contain spying functions (such as a packet sniffer) or backdoor functions that allow a computer, unbeknownst to the owner, to be remotely controlled from the network, creating a "zombie computer". The Sony/BMG rootkit Trojan, distributed on millions of music CDs through 2005, did both of these things. Because Trojan horses often have these harmful behaviors, there often arises the misunderstanding that such functions define a Trojan Horse.

Trojans implementing backdoors typically setup a hidden server, from which a hacker with a client can then log on to. They have become polymorphic, process injecting, prevention disabling, easy to use without authorization, and therefore are abusive