The ciphercoin premium plugin adds some features to the wp limit login attempts plugin. At the moment, the extra included functionality includes:
Unbreakable captcha: Commonly WordPress security breaking by using WordPress brute force tools like wpbf. An unbreakable captcha system will stop automated access. We added a random background in the captcha. So captcha breaking is not possible.
Unlimited installation license per user
You can use the pro version on unlimited websites.