Microsoft Safety & Security Center provides a free online security scanners, tools, and safety guidelines for your PC. Its password checker allows you to check the strength of your password. For more security of your accounts, you can check out your passwords at this site. The strength of a password depends on the different types of characters that you use, the overall length of the password, and whether the password can be found in a dictionary i.e. you password should contain upper, lower cases and special symbols as well. It should atleast be 8 character long.