Declan McCullagh writes that some of today’s new spam-blocking programs may actually wreak e-mail havoc. These programs use “challenge-response” technology, which requires human non-spammers to click a link or type a word in a box to make sure their e-mail gets to you. Apparently, much of this software is poorly designed, forcing individuals well-known to the recipient to continually respond to the “challenge.” What a hassle, especially for mailing list operators.