Registering for an account at any web site almost always requires an email address, and some people like to use a secondary address they don’t really care about instead of their real email address to avoid spam. If you do this, don’t use a Hotmail (Update: or other free webmail) account.
Microsoft shuts down Hotmail accounts that haven’t been logged into after nine months. So if you registered for your Gmail account two years ago and used your Hotmail address as your secondary email address and never logged back in, you’ve put your Gmail account at risk.
Here’s how: If your Hotmail account gets shut down due to inactivity, someone else can open a new one using your Hotmail address. Then, if that someone else requests a password reset from Gmail, it goes to that address, and that someone can get into your primary email account. This is how Twitter employees’ Gmail accounts got broken into last week.” (Smarterware )