Don’t reveal personal details to strangers or just-met “friends”.
The speed of Internet communication is often mirrored in rapid online acquaintanceships and friendships. But it is important to realize that you don’t really know who these people are or what they are like in real life. A thousand miles away, you don’t have friends-of-friends or other references about this person. Be also wary of face-to-face meetings. If you and your new e-friend wish to meet in person, do it in a public place.
Bringing a friend along can also be a good idea. One needn’t be paranoid, but one should not be an easy mark, either. Some personal information you might wish to withhold until you know someone much better would include your full name, place of employment, phone number, and street address (among more obvious things like credit card numbers, etc.) Needless to say, such information should not be put on personal home pages. (If you have a work home page, it may well have work contact information on it, but you needn’t reveal this page to everyone you meet in a chat room.).
For this and other reasons, many people maintain two personal home pages, a work-related one, and an “off duty” version. In the commercial sector, too, beware “fast-met friends”. A common “social engineering” form of industrial espionage is to befriend someone online just long enough to get them to reveal insider information.
Remember that you decide what information about yourself to reveal, when, why, and to whom.
Don’t give out personally-identifiable information too easily. Just as you might think twice about giving some clerk at the mall your home address and phone number, keep in mind that simply because a site asks for or demands personal information from you do not mean you have to give it. You do have to give accurate billing information if you are buying something, of course, but if you are registering with a free site that is a little too nosy for you, there is no law (in most places) against providing them with pseudonymous information. (However, it would probably be polite to use obviously fake addresses, such as “123 No Such Street, Nowhere, DC 01010″.