Many, many millions of people are on the Internet, and because one of them is you, it would be nice to know that the rest of them couldn't go snooping through your files and e-mail messages. Whether you know it or not, you already use at least one security procedure to prove that you are, who you say you are, online.

Your ISP (Internet service provider) gives each user an account,  like a bank or credit account. The account has your user name and a secret password associated with it.

Your user name, user ID, login, or logon name,  is unique among all the names assigned to your provider's users. It's also your e-mail address, so don't pick a weird name or something too common and easy. A weird name makes it difficult for your correspondents to remember your email address, while an easy name allows spammers to auto-generate similar names and thus find yours.

Your password is secret, or should be, and is the main thing that keeps out snoopers. Don't use a real word or a name. Never tell anyone else your password. Particularly, don't tell anyone who claims to be from your ISP - they're not. Change your password from time to time, using the procedure that your ISP decrees.

You can also prevent anyone from reading your messages by encrypting them in a secret code with a program like PGP (Pretty Good Privacy) from http://www.pgpi.org.

Many sites offer encrypted transactions for form submittals and credit card purchases. These sites usually have URLs starting with <https> rather than <http>. The <s> stands for <secure>. Your browser indicates whether a page offers security by showing a key or a closed padlock when the connection is a secure address.