The internet provides all sorts of amazing opportunities. It also provides a wonderful way for people to reach you to commit crime against you. There are several types, of which I know about:

a. Nigerian 419 Fraud. A "Get Poor Quick" Scheme!
An email (sometimes a letter or fax) arrives asking you to help someone get $30,000,000 or so out of a country (eg Nigeria but other countries too). The schemes can indicate a degree of illegality (eg Someone died and has no relatives: Please pretend to be a relative to help us get the cash). One trick they do is send you a cheque for you to clear for them "as proof of good will". You let the cheque clear and give them the money. 3 weeks later, the "cleared" cheque bounces... and you've lost £10,000. If you visit them to dispute the matter you can be either kidnapped for ransom or killed. Don't mess with these guys.

b. "Microsoft Windows XP Professional only $50, Adobe Photoshop 7.0 $60"
Sorry, but these unbelievable prices shouldn't be believed. You might not get any software at all, and if you do it will probably be a pirate copy. If you are so incredibly lucky as to get genuine software it was probably stolen! Don't bother with these "deals"- they aren't worth it.

c. "Shares in Company XYZ have doubled in value". The basic plot here is to get you to invest in shares in a small no-hope company. The fraudsters buy lots of shares. They then get others to buy shares (sometimes at inflated prices) so that the share price goes up. They then sell a the higher price, leaving the victims with shares that are now worth very little.

(I'll do more of these when I have time- but until then go to Scambusters)

For general information try http://www.fraud.org/