Spyware, viruses, worms, and Trojan horses are among the most common types of computer malware, or malicious software. They all use different methods to gain access to your computer, but they're all inherently evil; you must protect yourself against all of them.
A virus is a small piece of computer code that usually enters your computer hidden inside a larger program. The virus runs when you open the file that carries it, and it performs some kind of unwanted (and often damaging) action. Like a biological virus, many computer virus programs also create copies of the virus code and hide them inside other programs and data files; when a user sends a copy of the host file to another user, the virus infects yet another computer.
Boot sector viruses are a sub-category of virus that attacks the section of the hard drive that contains the programs that run when you turn on the computer, before Windows (or some other operating system) loads.
E-mail viruses travel as embedded code or attached files in e-mail messages. When you open an infected message, the virus runs. Many e-mail viruses also copy themselves and send copies to all of the names in the e-mail program's address book.
A worm is a program that attacks computers through security defects in common programs like Windows and Outlook. As they move through the Internet, some worms perform other unwanted tasks, such as altering Web pages and damaging utilities.
A Trojan horse is a program that is disguised as something other than its real identity. For example, you might discover an attractive-sounding game or music file, or even an anti-malware utility on a Web site. But when you download and install the program, it does something entirely different, such as erasing the files on your hard drive, or changing the home page on your Web browser to a site that carries advertising or offensive content.
Many of these programs do an excellent job of camouflaging themselves. It's easy to infect your computer with malware, but it's often extremely difficult to get rid of because the malware has moved in and taken control.
Even if you don't have any visible evidence, it's entirely possible that your computer has been infected. And new attacks are happening all the time. So antivirus software is essential. If your computer doesn't already have an active antivirus program in place, install one now.
A good antivirus program includes both a full-time monitor that detects viruses before they can install themselves on your computer, and a scanning utility that examines your system for previously undetected infections.
Microsoft has tested most of the antivirus programs that are currently available, and posted a list of them at http://www.microsoft.com/athome/security/viruses/wsc/en-us/flist.mspx. Some of these suppliers offer free trial versions of their products, so you can test more than one before you make your choice. At least two, Avast (http://www.avast.com) and Grisoft (http://www.free.grisoft.com) offer free versions for personal use.
To be sure your regular antivirus program hasn't missed anything, you should also run an occasional scan with a second antivirus package from a different supplier. You can run free online virus scans from Trend Micro (http://www.trendmicro.com/hc_intro/default.asp), BitDefender (http://www.bitdefender.com/scan8/ie.html), or Panda Software (http://www.pandasoftware.com/activescan/activescan).
Antivirus programs are usually effective in keeping your system clean, as long as you remember to install updates as soon as they become available (most programs can run automatic updates every couple of days). But to be doubly sure, take these precautions:
Don't open files attached to e-mail messages unless you know and trust the person who sent it to you. If you have already opened a suspicious file, run an antivirus scan as soon as possible. In particular, don't open any file with one of these file extensions:
If you receive an e-mail with an attached file with one of these extensions from somebody you know and trust, don't open the file. Send a reply asking the originator to compress the original file and send it as a .zip file.
Don't install or run programs you downloaded from unknown sources. Games, music files, and pornography are especially popular virus carriers.
Turn off your computer or unplug the network connection when it's not in use. Like the proverbial rust, crackers and other online intruders never sleep.
Find and install all the available updates and patches for Windows, your antivirus program, and all the other programs installed on your computer. When software developers discover security threats or other problems, they usually provide fixes or patches through their Web sites. Look in each program's Help menu for an "About" command that displays the address of the developer's Web site.
Back up your files!
Spyware is software that collects information about you and your computer and sends it to people who want to use it without your permission. Spyware includes programs that might do any of these unwanted actions:
Capture and forward your keystrokes
Copy images of your screen
Forward lists of the hardware and software installed in your computer
Replace your Web browser's home page with a page that contains advertising, pornography, or political messages
Replace the content or banner ads in Web sites with the Spyware author's own advertisements
Collect account names, passwords, and other personal information
Track your online activity to send you targeted advertising, either as e-mail, or in unwanted pop-up windows
Spyware usually loads itself into your computer without your knowledge or permission, often hidden inside other programs. Just because an online ad or e-mail offers something like a "free computer tune up," the real program does not always provide a truly useful service.
To protect yourself against the damage that spyware can do, you must find and remove any spyware that has already made its way into your computer, and keep new spyware out. Several anti-spyware utilities can perform all of these functions: Ad-Aware (http://www.lavasoft.com), Spybot Search and Destroy (http://www.safer-networking.org), and Windows Defender (http://www.microsoft.com/athome/security/spyware/software) are all effective against the most common spyware.
For more advice about removing spyware, including specific instructions for killing and removing programs that don't always respond to the all-purpose anti-spyware utilities, consult the list at http://www.pchell.com/support/spyware.shtml.