Basic Preventative Steps:
There are a few "golden rules" for maintaining a secure Battle.net account. They're simple and straightforward, but they can help ensure that your account information doesn't get into the wrong hands.
 Never give our your account information
 Practice good email security
 Be mindful of phishing scams
 Grab a Battle.net Authenticator
 
- Never give out your account information.
Sharing your account information with a family member, friend, or another player is an easy way to lose control of who has access to your account and increase the risk of compromise -- no matter how well you might know the person you’re sharing your login information with. Keep in mind that even if you practice optimum Internet security at home, you can't control how another person will make use of your account information…or how secure their own computer system might be.

- Practice good email and password security.
Ensuring that your registered email address is secure is a very important part of keeping your Battle.net account secure. Your registered email address not only serves as a primary point of contact with Blizzard Entertainment, but it also functions as your Battle.net account name. For this reason, you may want to consider creating a unique email address for your Battle.net account, and we *strongly* recommend using a password that you don’t use for any other online service.

- Be mindful of phishing scams.
Phishing scams are designed to trick you into giving out your account information, and they'll usually come in the form of emails or in-game messages that appear to be sent by Blizzard employees. Sometimes these messages encourage you to visit a malicious website (which might contain a web form for you to fill out or even embedded software that can steal your login information). In other cases, you may be asked to reply with your account name and password.