Aiming to cut spam sent to its Hotmail and MSN users, Microsoft is developing a new generation of proofing tools that will augment filters.

Proofing technology requires the sender to authenticate themselves - the idea being that a spammer will not have the time to do so for every email sent.

Microsoft believes that current technologies put an unjust burden on the consumer by requiring users sending mail to reply to an email or to visit a web page.

Ryan Hamlin, Microsoft's general manager for anti-spam technology and strategy, will tell delegates at an email conference in San José, California, later today about technology currently being developed by the company.

The technology will authenticate the sender by giving his or her computer a hash algorithm - effectively a little software puzzle that takes some time to solve.

"We have this general idea about a 20-second CPU cycle," Hamlin told vnunet.com. Consumers "will not notice it. But if you are a spammer getting 10,000 challenges, you are certainly going to notice it. You won't be able to handle it.

"As soon as we have enough of these proof tools out there, that's when we can really lock down the filters."

The proofing technology is scheduled to be available within the next 12 months.

Hotmail currently blocks 2.7 billion spam messages per day, or 77 per cent of all messages sent to its account holders. Hamlin estimates that roughly 10 per cent of spam still gets through.

The new proofing technology will allow the company to reach its goal of blocking 98 to 99 per cent of all spam for MSN and Hotmail users in the next two years, he said, to make spam only the occasional message.