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Frequently Asked Questions

This FAQ answers questions about computer viruses and other Internet security threats. It also tries to clear up some common misconceptions about viruses and e-mail.

Why should I care about computer viruses? Isn't all this just a bunch of hype drummed up by marketing departments for antivirus software companies?

Sadly, no. Since the rise of the Internet, more and more computer users have been flooded with viruses, worms, trojan horses, spam, phishing attacks and other security threats. (To learn more about what these terms mean, check out the Virus Laboratory.) And when a virus hits, everyday people end up having to put in large amounts of time and effort to get their computers operational again.

Some people have had to buy replacement chips or pay for a repair shop to get their systems back in operation. And some of those people have lost data they will never be able to replace.

Most viruses are well-known and virtually every current antivirus program can handle them. But a lot of people don't have antivirus software, and many of those who do have it don't use it regularly or keep it updated. So they lose time, money, and irreplaceable data when viruses hit simply because they don't take basic precautions to protect themselves.

The virus threat is not going away. As we have already seen, there are a lot of people out there who would just love to create havoc with their virus creations. Your job is to protect yourself.

What is a computer virus?

A computer virus is a program designed to spread itself by first infecting computer files and then making copies of itself. Viruses usually operate without the knowledge or intent of the computer owner.

What kind of files can spread viruses?

Viruses have the potential to infect any type of executable code, not just the files that are commonly called 'program files'. For example, some viruses infect executable code in the boot sector, or the section of a hard disk that contains operating system and file information. Another type of virus, known as a 'macro' virus, can infect word processing and spreadsheet documents that use macros. And it's possible for HTML documents containing JavaScript or other types of executable code to spread viruses or other malicious code.

Since virus code must be "run" to have any effect, files that contain pure data are safe. This includes graphics and sound files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt files. For example, just viewing picture files won't infect your computer with a virus. The virus code has to be in a form, such as an .exe program file or a Word .doc file, that the computer will actually try to execute.

How do viruses spread?

When you start a program that's infected by a virus, the virus code will also run and try to infect other programs, either on the same computer or on other computers connected to it over a network. And the newly infected programs will try to infect yet more programs.

When you share a copy of an infected file with other computer users, running that file may also infect their computers; and files from those computers may spread the infection to yet more computers.

Some viruses, known as 'multipartite' viruses, can attack both the boot sector and the executable files at the same time. This type of virus can keep re-infecting a system over and over again.

What do viruses do to computers?

Viruses are software programs, and they can do the same things as any other programs running on a computer. The actual effect of any particular virus depends on how it was programmed by the person who wrote the virus.

Some viruses are deliberately designed to damage files or interfere with your computer's operation, while others don't do anything but try to spread themselves around. But even the ones that just spread themselves are harmful, since they damage files and may cause other problems in the process of spreading.

Note that viruses can't do any damage to computer hardware. They won't melt down your CPU, burn out your hard drive, cause your monitor to explode, etc. Warnings about viruses that will physically destroy your computer are hoaxes, not legitimate virus warnings.

What is a Trojan Horse program?

A type of program that is often confused with viruses is a 'Trojan horse' program. This is technically not a virus, but simply a program (often harmful) that pretends to be something else.

For example, you might download what you think is a new computer game. But when you run it, it deletes files on your hard drive. Or the third time you start the game, the program e-mails your saved passwords to somebody on the Internet.

Note: Simply downloading a file to your computer won't activate a virus or Trojan horse. You have to execute the code in the file to trigger it. This could mean running a program file, or opening a Word/Excel document in a program (such as Word or Excel) that can execute any macros in the document.

What's the story on viruses and e-mail?

You can't get a virus just by reading a plain-text e-mail message. What you have to watch out for are messages that contain embedded executable code (i.e. JavaScript in an HTML message) or messages that include an executable file attachment (i.e. an encoded program file or a Word document containing macros).

In order to activate a virus or Trojan horse program, your computer has to execute some type of code. This could be a program attached to an e-mail, a Word document you downloaded from the Internet, or something received on a disk. There's no special hazard in files attached to e-mail messages: they're no more or less dangerous than any other file.

What can I do to reduce the chance of getting viruses from e-mail?

Treat any file attachments that might contain executable code as carefully as you would any other new files — save the attachment and then check it with an up-to-date virus scanner before opening the file.

If your e-mail software has the ability to automatically execute JavaScript, Word macros, or other executable code contained in or attached to a message, you should disable this feature.

If an executable file (with extensions like .EXE .COM or .VBS) shows up unexpectedly attached to an e-mail, you should delete it unless you can positively verify what it is, who it came from, and why it was sent to you. Just because an e-mail appears to come from someone you trust, this does NOT mean the file is safe or that the supposed sender had anything to do with it.

How do I protect myself from viruses?
  1. Install antivirus software from a well-known, reputable company. UPDATE it regularly, and USE it regularly. New viruses come out every single day — an antivirus program that hasn't been updated for several months will not provide much protection against current viruses. If you're looking for a free antivirus program, try HouseCall.
  2. In addition to scanning for viruses on a regular basis, install an 'autostart' scanner (included in good antivirus software packages like Trend Micro Internet Security) and configure it to start automatically each time you start your computer. This will protect your system by checking for viruses each time your computer accesses an executable file.
  3. Virus scan any new programs or other files that may contain executable code before you run or open them, no matter where they come from. There have been cases of commercially distributed disks and CD-ROMs spreading virus infections.
  4. Some antivirus programs aren't very good at detecting Trojan horse programs, so be extremely careful about opening text-only files and Word/Excel documents from unknown sources. This includes downloads from Web sites that aren't well-known or don't have a good reputation, and executable files unexpectedly received as attachments to e-mail or during an online chat session.
  5. If your e-mail software has the ability to automatically execute JavaScript, Word macros, or other executable code contained in or attached to a message, you should disable this feature.
  6. Be extremely careful about accepting programs or other files during online chat sessions. This seems to be one of the more common means that people wind up with virus or other Internet security problems. And if any other family members (especially younger ones) use the computer, make sure they know not to accept any files while using chat.
  7. Backup your computer files regularly. Some viruses and Trojan horse programs will erase or corrupt files on your hard drive, and a recent backup may be the only way to recover your data.
  8. Ideally, you should also back up your entire system on a regular basis. If this isn't practical, at least backup files that you can't afford to lose or that would be difficult to replace: documents, bookmark files, address books, important e-mail, etc.
How do I deal with a virus infection?

First, keep in mind, that just because your computer is acting strangely or one of your programs doesn't work right, does NOT mean that your computer has a virus.

  1. If you haven't used a good, up-to-date antivirus program on your computer, do that first. (If you're looking for a free antivirus program, try HouseCall.) Many problems blamed on viruses are actually caused by software configuration errors or other problems that have nothing to do with a virus.
  2. If you do get infected by a virus, follow the directions in your antivirus program for cleaning it. If you have backup copies of the infected files, use those to restore the files. Check the files you restore to make sure your backups weren't infected.
  3. For assistance, check the Web site and support services for your antivirus software.

Note: In general, drastic measures such as formatting your hard drive should be avoided. They are frequently useless at cleaning a virus infection, and may do more harm than good unless you're very knowledgeable about the effects of the particular virus you're dealing with.

What is the best antivirus software available?

We admit that we're a little biased — we've designed Trend Micro Internet Security to be the best product on the market. But don't just take our word for it — see what indepdent reviewers have said about antivirus software:

(This FAQ was adapted from the Computer Virus FAQ for New Users with permission from the author, Nick, who kindly requests that you not email him with virus questions.)