........With computers, total security can be achieved with absolute isolation, but if you use your computer for communication of any kind through the internet, then you depend on password security everywhere. While you have little control over how well various online communities and companies protect your password, you do have a great deal of control over the passwords you use.
If you’re a target and if the password for your bank account or your PayPal account can be broken with only a few days of computation, then it’s cost-effective for a mal-intentioned hacker to make the attempt. If your password requires several years of computation, it’s probably not worth it. If your password is so long and so complex that it would take centuries to crack, then you have achieved a practical level of security.
Maximum PC | Future Tense: The Universal Password