A common fraud, called “phishing”, sends messages that appear to be from a bank, shop or auction, giving a link to a fake website and asking you to follow that link and confirm your account details. The fraudsters then use your account details to buy stuff or transfer money out of the account. These fake sites can be hard to spot, so no reputable organization will send a message requesting your confidential information.
When you use an on-line account, type the website address you have been given from a trustworthy place (from your bank statement, for example) into the browser directly so that you know you are going to the correct place. You can always save it as a bookmark/favourite