Missigua Locator is a hostile web crawler program which collects e-mail addresses (which are then used by the person running the crawler to spam). It does not follow the Robots Exclusion Standard.
It identifies itself as "Missigua Locator 1.9".
This is a program anyone can get their hands on and run, so IP based blocking is sort of out of the question. However, the software (as is) does identify itself correctly using User-Agent when crawling - but it doesn't care about robots.txt.
See HOWTO stop automated spam-bots using .htaccess on how to block them