User Enumeration is a method hackers and scanners use to get your username. This plugin stops it.
Even if you are careful and set your blogging nickname differently from your login id, if you are using permalinks it only takes a few seconds to discover your real user name. This plugin stops user enumeration by and produces a 'forbidden' page.
This pulgin goes a step further than can be achieved with .htaccess alone, as it writes the enumeration attempt in your system log so you can use (optionally) fail2ban (or other log monitoring tools) to block the probing IP.