Unfortunately most of us seem to be victim to spam email on a daily basis. Sometimes it can be harmless junk mail with someone trying to sell you something but other times it might be a bit more sinister, with the sender trying to steel personal details such as addresses, bank / card details and login / passwords.
Once a hacker has obtained your login details to a certain site, Amazon, for example, they can then change the delivery address details and purchase products using the card or PayPal account that is linked to your Amazon account. You may not be aware of it until you next come to use your card. If you receive any suspicious email claiming to be from a company you use, asking for details or for you to log in to their site, do not do it until you have confirmed it is genuine, either by calling the company or visiting the website directly not through the link in the email.