You receive an email saying you won an iPhone. When you click the link in the email, you were asked to enter your credit card number
Don't answer this link with your personal information. These links typically bring you to websites where hackers will take your information and ruin your identity and take your money. Stay away from words such as "FREE".
Emails like this sometimes contain images and data showing they are a part of a company giving away 'free' items. For example Argos could be giving away a new iPhone and all you need to do is enter address and credit card information. Which is already unsafe. Avoid anything free on the internet even through trusted company because there are ways they can scam you