Is it true that some one is able to steal and use your account and what can we do to prevent?

You need to explain a little further about what account someone is able to steal and use. Your personal account? Your Yahoo account? Your credit card? What? If you don't give someone your password or details about how to use your account, it would take a very determined hacker to get your password. Making that password something difficult to get is the best way to prevent someone else using it. That means don't use your social security number, your birthday, your dog/cat/bird's name or your mother's maiden name, or your child's name/birthday. You should use alpha-numeric passwords anyhow, they are the hardest to break.