Your Guide to Spyware

Trojans
A Trojan, or rather its full name, “Trojan Horse” is an allusion to the epic tale of the ancient city of Troy and the Greek’s Trojan Horse. In the siege of Troy, the Greeks left a large wooden horse outside the city. The Trojans were convinced that it was a gift, and brought the horse within the safety of the city walls. What the Trojans didn’t know was that horse was hollow, and hidden inside were a small number of Greek soldiers. After nightfall, they snuck out of the horse and opened the city gates of Troy, allowing the Greek army to enter and pillage the city.

Trojan horse programs work in much the same way; they may appear useful or interesting at first glance to an unsuspecting user, but like the Greek’s Trojan Horse, it is certainly not the case. A Trojan is a form of malware that cannot engage in self-replication, but can be harmful when executed. A Trojan can be deliberately attached to otherwise useful software, distributed on its own posing as useful software, or can be spread through a variety of download methods over the Internet (i.e. email, IM, and file sharing) by tricking users to open it. Note that Trojans cannot spread by their own accord, they must be “invited” into systems, per say. They rely on unsuspecting users to pass them around. If the Trojan poses as a harmless joke or screensaver, for example, the idea is that unsuspecting users will pass it along to their friends. It’s yet another reason to ignore those chain emails with “re: re: re:” in the subject header.

To further complicate matters, some Trojans can spread or initialize other forms of malware. When used in this fashion, they are referred to as “droppers”. Other common features of a Trojan can include (but are not limited to) file deletion, subtle to major file corruption, spying activities, and data theft. Last but not least, Trojans can install backdoors in systems in order to turn them into zombie computers, which can perform any one or even many of the tasks just listed, as well as email spamming and DoS or DDoS attacks.

Worms
The name “worm” was taken from a 1970’s Sci-Fi novel, The Shockwave Rider by John Brunner. While working on a research paper on experiments in distributed computing, researchers noted similarities between their software and the program described in the novel, and thus adopted the term.

A worm is a form of malware that is similar to both a virus and a Trojan. It’s similar to a virus in that it engages in self-replication, and is somewhat similar to a Trojan in that it can be, and usually is, a completely self-contained program. Unlike a Trojan, a worm does not need to be executed by the user; it can execute and jump around from system to system on its own accord because of its ability to self-replicate. It can clog up systems, as well as networks, and bring both to their knees. Other features can include file deletion, email spamming (with or without file attachments), and DoS or DDoS attacks. Like Trojans, worms can install backdoors in systems in order to turn them into zombie computers, which can perform any one, even many, of the tasks just listed.

For a brief time, programmers attempted to use worms as useful system patching tools to plug security holes and other various vulnerabilities. This, however, ultimately backfired. These types of worms often clogged up networks more effectively than intentionally malicious worms, as well as doing their work on systems without the user’s explicit consent. In the course of applying these patches, systems suffered from sudden and unexpected reboots, thus effectively causing data loss in open or unsaved files, as well as causing connection problems with the rebooting of a server. Today, the potential legitimate uses of worms are now the talk of computer science and AI theory.