Fraud is rampant on internet. It is everywhere that you look. When you are lurking in newsgroups you will find hundreds of messages inviting you to spend money here, there and everywhere. You'll get email demanding your time, attention, and, of course, money for something. Surfing web will turn up many sites with some incredible offers which, of course, just happen to require your credit card number - but don't worry, they "just need it to validate your age" (or whatever) - DON'T GIVE THEM YOUR CREDIT CARD NUMBER UNLESS YOU ABSOLUTELY KNOW IT'S SAFE.
The web is a media of communication. It allows everyone to communicate with anyone for price of a computer, phone line and internet service - and even most of that can be gotten for free if you try. This is perhaps most wonderful invention in history of man to date for it's sheer power of getting us all just to talk to each other, but there are dangers.
In a way, it's just like any other part of life. However, what internet does is to allow you to communicate (and be communicated with) exceptionally fast. Where else could you surf a hundred sites, receive 200 emails and examine 250 newsgroup messages all in one evening?
Some of schemes that you will need to be on lookout for include:
Pyramid schemes galore. These are things that say "send a dollar to a bunch of people with your name and address". They are all illegal (in spite of what they claim) and unethical. You will get ripped off and if you partake you are breaking law.
Startup companies which offer stock or "points" - these are not frauds, per say, but vast majority of these will never pay anything to anyone. For example, many pay-to-surf programs at their beginning will not pay anything. Instead, you will get points or stock, with promise of money down road if they (a) go public or (b) get lots of people signed up or whatever. Beware - you are taking a risk to never get anything.
Credit card fraud - be very careful with your credit card number on web. DO NOT EVER send it in email or post it in a newsgroup. And DO NOT USE YOUR DEBIT CARD FOR ANYTHING ON THE WEB. That comes directly out of your checking account - you may get it back from bank if you can prove fraud, but at least with a normal credit card you are risking banks money and not your own.
Multi-Level Marking (MLM) - I'm sure there are good MLM companies out there, but they really only tend to benefit those who get in early. Those on bottom wind up supporting those on top, then whole thing loses steam and falls apart. Of course, those who do get in early make a lot of money.