“ A captcha (meaning 'Completely Automated Public Turing test to tell Computers and Humans Apart') is difficult for automated script to solve, but relatively easy for a human. This prevents automated account creation, a favourite strategy for spambots. ”

“ Changes Antispoofing enabled Implemented 17 October 2006, antispoofing compares new names to existing accounts at registration to prevent impersonation. One example logged during the trial run is 'Sp1arka', too similar to Splarka. Blocked registrants are told that "The name "new_username" is not allowed to prevent confusing or spoofed usernames: old_username. Please choose another name."
'@' prohibited Since 26 September 2006, new usernames containing the '@' character cannot be registered. The change affects all recent versions of MediaWiki, including those used by third parties. ”