There should be a slash after the "Disallow:" (as quoted in the article above). Otherwise, you're inviting them to spider your site.
As I wrote above, the real BecomeBot seems to be behaving properly as long as you use the "long" form of the robots.txt, i.e. with one Disallow: statement for each bot you want to block.
Authored by: Dirk on Monday, August 28 2006 @ 09:37 CEST