The Penny Black Project - Outsmarting Spam

Microsoft has a plan in place to put spam into history: increase the cost of sending multiple messages. Currently, it costs the same to send a message to one or more persons. With new software, code-named Operation Penny Black, for every email sent the sender's computer would require to solve a complex math problem that takes 10 seconds. It wont be a problem for sending a few mails but spammers, who send millions of emails, will certainly be haeding for trouble.

Source: India Today (feb 23, 2004)