You may have been fooled. Some 3rd party site can invade your privacy pretty easily. They can get your e-mail account and password. For instance, you are a member of QJ.net, the 3rd party website can get your account and password from here, just requesting a reset on password. It can be done with your email they invaded.
This is nothing technical, it doesn't involve any hacking, it's really a social engineering. Social engineering is the practice of obtaining confidential information by manipulation of legitimate users. Here's how it works, when you register to a site like gamespot.com, they are gonna ask you to choose your username, password, email address, etc. Most 3rd party site put the username field first, then email address, then password. You are most likely to use the password same as your email account that way.
Sites like walmart.com, bestbuy.com, gamespy.com, I'd say it's pretty safe. Just be careful on what site you go to and register an account. Always use different password for each different site.
This concludes the information. I hope this helps you to protecting your email account.