while funny, its unlikely that it was written by cleese.
seems to have been first posted in 2007 here:
http://tartfromhell.com/2007/03and then a few month later by John Humberstone, found here:
http://www.nlpconnections.com/chill-out-room/2318-security-alert-status.htmla thread about this:
http://message.snopes.com/showthread.php?t=70255