Spam will be a thing of the past in two years' time, Microsoft boss Bill Gates has promised.
Spammers - senders of bulk e-mail that mostly offers dubious products or pornography - were innovative, he said.
However, a three-pronged strategy
would soon stamp out the problem, he said in remarks at the World Economic Forum (WEF) in Davos.
He hailed search technology firm Google as a "great company"; its approach reminded him of Microsoft 20 years ago.
Microsoft's chief, estimated worth $46bn, is the US' richest man
But he also predicted that Microsoft search technology would soon outpace that of its rival.
Mr Gates, by now a fixture at the annual WEF's meeting of business leaders and top politicians, said a lot of progress had been made during the past year to stop spam e-mail.
"Lots of mail you get is from people on your contact list. So what's the problem? Strangers!"
Filters could do a lot to sort spam from real mail, Mr Gates said: "Does the e-mail say it's about 'enlargement' - that might be spam."
But by adding random words in subject lines and replacing text with pictures,
spammers were trickier to catch and in the long run filters would "not be the
More promising were "human challenges" - forcing the sender to solve a puzzle,
or the computer sending the e-mail to do a simple computation.
"That's easy for a machine sending a few e-mails, but gets very difficult and
expensive for a computer sending lots of spam," Mr Gates said.
But ultimately, Mr Gates predicted, spam would be killed through the
electronic equivalent of a stamp, also known as "payment at risk".
This would force the sender of an e-mail to pay up when an e-mail was rejected
as spam, but would not deter senders of real e-mail because they could be
confident that their mail would be accepted.
"Microsoft is pursuing all three approaches, and spam will soon be a thing of the past," Mr Gates asserted.
Google vs Microsoft
Asked whether Microsoft missed the boat in the field of search technology, Mr Gates admitted that he had to take the blame for losing out to Google.
"We took an approach that I now realise was wrong," he said.
"Our strategy was to do a good job on the 80% of common queries and ignore the other stuff."
Mr Gates claimed that Microsoft was better on the 80% of common queries,
although Google was "pretty good" as well.
"But that's not what counts. It's the remaining 20% that counts... because
that's where the quality perception is."
Google was "way better", he said, for people investigating a rare disease,
exploring a hobby, or searching for a specific restaurant.
He praised the "high level of IQ" at Google's research team, but said "we will
X marks the box
In his wide-ranging remarks, Mr Gates described the first generation of his
company's Xbox video games console as a "pretty good first shot", that would
allow it "to play again".
Gates and his wife have set up a charitable foundation
"We are a fairly strong number 2 to number 3, and a weak number 2 to number 1.
But we have gained good credibility... and shown that we are hardcore about
Game software makers were now taking Microsoft seriously, and the next Xbox
generation in two or three years' time would be "mind-blowing".
The future of computing
And anyway, in a decade from now, "we will laugh at personal computing as we
In a world of "seamless computing" everything would be digital, flexible and
personalised, and driven by software not hardware.
"What is holding things back right now is software," Mr Gates said, before
adding with a smile: "At least I hope so, otherwise we are overspending to the
tune of billions."