Most computer users know that the Internet has its “dark side”. Our online world brings issues of credit card and identity theft and junk mail. But how many computer users are unwitting accomplices to such activities?

It is possible that your computer, or a friend’s computer is being used to send spam, harvest e-mail addresses for spam, make purchases using stolen credit cards or take part in a denial of service (DoS) attack, where an army of computers shuts down a Web site by flooding its servers with HTTP requests.

Recently, a pilot program scanned more than a million computers, finding over 29 millions instances of spyware, an average of nearly 28 spyware items per computer.

How does this happen without your knowledge? Examples like those above are usually the work of a “trojan”, a small program that can be unknowingly installed on a computer and then accessed by another computer over the Internet. Together with programs called “spyware”, “adware” and viruses, trojans are a part of a group collectively known as “malware” or “pestware.” While the majority of such programs are annoying and nothing more, they have the potential to be quite nasty.

Spyware: Who’s Watching Your Online Moves?

Spyware programs range from annoying to the dangerous, including keyboard loggers and screen capture applications that can steal passwords and other sensitive information. These programs are sometimes bundled in with shareware or freeware programs that can be downloaded from the Internet. Often times they claim to be helpful utilities that also carry a more sinister side.

Many of the programs are marketed as legitimate tools for keeping tabs on children online. One program called “Activity Logger”, for example, connects to the Internet, records the URLs of sites visited and the keystrokes from e-mail and chat applications. It will also capture screenshots that can be made into a slide show.

Adware: Caught in a Marketing Nightmare

Adware is software that displays advertisements to computer users. Some of the most strict definitions of adware include applications that are sponsored for their free use. One of the most popular examples is WeatherBug, which offers a free version of weather software and comes wrapped in a skin that displays advertising. While older versions of WeatherBug had rather significant privacy issues, newer versions are pretty straight forward: you see the ad, but you get the weather. Is this adware? In the most strict sense, many people say it is. But to some computer users, the tradeoff seems fair. Hotmail, Yahoo Mail and AOL’s Instant Messenger are among other software programs and services that display ads to their users in exchange for free usage. Many of these programs off advertising-free versions for a price.

More annoying among adware watchers is Gator, which now goes by the name Claria Corp. Gator was controversial from the start. It began in 1998 offering e-wallet software. But it reports your Web surfing habits back to its parent company, which then sends you advertisements targeted according to your data. The vast majority of people consider it a pest, especially because the software is often bundled with other, more useful software. As annoying as it is, Gator is not very malicious.

As for adware that reports personally identifiable information, user tolerance varies. Some people don’t want any information revealed, such as tracking the sites you visit. Others draw the line at logging IP addresses.

Trojans: RATS That Can Control Your Computer

Like the horse of the story, a trojan carries with it an unexpected surprise. Trojans do not replicate like a virus, but they do leave behind a program that can be contacted by another computer. From there, they can do just about anything. While it’s possible a trojan can be used to take control of a computer, the most common trojans are “dialer” programs. Dialers are used without your knowledge to make international or premium calls (900-type numbers) from your PC. That’s more than an annoyance; it can get expensive.

Trojans are also known as RATS (remote access trojans) and they are most often hidden in games and other small software programs that unsuspecting users download then unknowingly execute on their PCs.

A trojan specially annoying is “CoolWebSearch”. Once it installs in your computer (exploiting security flaws in unpatched Windows systems), it “hijacks” Internet Explorer, changing its settings. For example, it changes the start page, adds new bookmarks, redirects the browser to another site when a page is not found, etc. This kind of browser hijacks are quite annoying, and unfortunately are becoming common.

Two other common trojans are known as “Back Orifice” and “SubSeven”. Back Orifice was originally developed as a remote administration tool. But it worked by exploiting holes in Microsoft software, which makes it a popular tool for nefarious applications. Both Back Orifice and SubSeven can be used to capture what is on a computer’s screen and what is typed in using the keyboard; they can be use to remotely control devices, such as opening and closing the CD drive; or to set up FTP, HTTP or Telnet servers on an unsuspecting user’s machine. Basically, anything that can be done with a computer can be done remotely using a trojan.

Viruses: Contagious Pests

For all the publicity viruses have gotten, they remain a serious threat. While viruses can potentially destroy a computer’s data, most of the widespread viruses have leaned more toward annoyance. The most famous are e-mail viruses that replicate and spread using e-mail addresses stored on a computer. They still cost computer users and their employers hundreds of millions of dollars annually.

The MS Blaster worm that caused havoc in the summer of 2003 exploited a vulnerability in the Remote Procedure Call (RPC) function of the Windows operating system. Anyone who did not install a patch issued by Microsoft was vulnerable, marking a new era in virus prevention for many Internet users. No longer was using care with e-mail attachments enough to keep you safe.

In our next article how to know if you are infected by spyware, we will talk about the symptoms caused by these programs, so you can be alert to find these pests.

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