Remember that most of the time you are using the Internet, whether it's receiving email or accessing a Web page, you are taking files from one computer and allowing them onto yours. Some of those files may be infected by viruses, which are the most prominent technological danger on the Internet.

Viruses are small programs that people write with the hope of causing trouble. Although some are just pranks or stunts, most are designed to intentionally damage or destroy your files or computer. It's pure vandalism, and viruses can cause especially big trouble because they are often written to exploit your connection to the Internet, spreading themselves automatically to infect other computers.

You can get viruses mainly in two ways: from file attachments to email messages you receive, or from files and programs you download from Web sites. Viruses and other computer crimes are a constant threat because many hackers (people who gain access to other people's computer files without authorization) consider it a challenge to create new and more dangerous programs. Although no complete protection exists, good habits, caution and common sense should keep you relatively safe if you follow these suggestions:

• Every computer should have a virus protection program, and you or your network administrator should be sure to get updates regularly to protect against new viruses.

• Only download software and files from reliable sites, such as the those of large, established companies, which usually check programs thoroughly before making them available for download.

• Be careful of opening any files that are attached to your emails, especially from people you don't know. Most viruses are in what are called "executable files"; in other words, they are programs that "execute" instructions for your computer to follow. In contrast, document files (such as a word processing document or a graphic) are simply displayed by other programs. It can sometimes be difficult to identify an executable file, but it helps to understand the concept of file formats and extensions. Many different file extensions are available for executable files, so in general, if you receive an attachment that has an ".exe" or a type of extension you don't recognize, don't open it unless you verify what it is.

Many viruses can copy themselves and automatically send out new infected messages to people in your email contacts list without you even knowing the message was sent. Don't let down your guard. Just because an email message comes from one of your friends, if it has a suspicious attachment, don't open it. Check it out first, by contacting your friend and your network administrator, or just delete it to be safe. Your friend may have no idea that he or she is infected.

• The Internet community is getting better and better about notifying people about new viruses found on the Net, so pay attention to warnings you may receive. The Internet is so popular now that you'll even see stories about major viruses on the TV news. Pay attention, but don't let your guard down; viruses can spread so fast that you may get the warning too late.

• Over the years, people have played a number of practical jokes by warning about fictional viruses just to scare people. Some of these pranks are very old, but they keep resurfacing as more new users gain access to the Internet. If you get a virus warning, go to a virus site (see links below) and make sure it's real before you pass it on to others, particularly before you send to many people or to an electronic mailing list. You'll be glad you did.

• If you encounter anything suspicious, contact your network administrator or other technical personnel right away. Again, better safe than sorry.

• Although it is an issue of concern mostly for your network administrator, you may want to be aware of issues involving hackers. You've probably read newspaper stories about hackers breaking into corporate or government computers and stealing data or making changes to Web sites. There's probably little that a hacker wants in your computers; then again, kids are known to play practical (or impractical) jokes. To protect against this possibility, your center may want to add security software to its LAN, including a firewall, which may block certain types of suspicious files coming through email or downloads.

It may not be necessary to explain all of this information to the kids in great detail, especially to younger kids. Give them some appropriate advice, and at least instruct them not to open attachments or download files from the Internet without checking with you first.