1. Never click on links in e-mails claiming to be from your bank, PayPal or eBay unless you have been expecting a mail. You can always access your account by typing in the URL of the website - if there is a problem with your account you will get a message there.
2. Always use different passwords for each website you are a member of.
If someone gets one of your passwords they will only have one, not a handful.
3. Check that you only enter your credit card details on a secure site - look for the padlock, grey-green protecting of the address bar in FireFox, and the https:// prefix to the web address.
4. Don’t believe what you read in your e-mails. Just because they are sent to your address does not mean they are true or genuine.
You can read more tips relating to staying safe online at my computer, business and internet blog.