Microsoft regularly targeted by hacking groups
In an e-mail sent to every member of the software giant's staff, Mr Gates said computer security was key to making its future products acceptable to consumers and businesses.
But others have questioned his sudden conversion, saying the change comes too late and ageing Microsoft products will be a problem for years to come.
Others have said the e-mail looks like a PR stunt, and is in stark contrast to Microsoft's attempts to limit the spread of information about the security failings of its products.
Security lessons
Mr Gates dubbed the new initiative outlined in the e-mail as "Trustworthy Computing", and said it had to become "the highest priority for all the work we are doing".
He warned that unless Microsoft products are secure and trustworthy no-one will risk using them for the kinds of web-based services it is betting its future on.
Anyone at Microsoft writing software who has to choose between adding new features or making them more secure, should choose security every time.
"Our products should emphasise security right out of the box, and we must constantly refine and improve that security as threats evolve," wrote Mr Gates.
Many Microsoft watchers have compared the mail to the moment in 1995 when it recognised that importance of the internet, and the announcement in June 2000 of the .Net initiative which updated this web-centred strategy.
Security failings
But others are more sceptical about the substance of the e-mail.
"It's about time, perhaps overdue," said David Smith, an internet strategist at research firm Gartner.
Mr Smith said before now Microsoft products have done much to undermine the security of the internet.
The biggest virus outbreaks of the last two years can all be traced to vulnerabilities in Microsoft software, especially its popular Outlook e-mail program.
The Code Red worm, which disrupted the lives of tens of thousands of net users, spread by exploiting problems with Microsoft's Internet Information Server.
Even XP, which Microsoft has declared its "most secure operating system ever", is not free of security failings.
In late December, eEye Digital Security discovered a hole in Windows XP which could have been used by malicious hackers to take remote control of a PC.
Even Scott Culp, Microsoft security manager, called it "a very serious vulnerability".
PR problem
The same Mr Culp criticised security researchers recently for their zeal in spreading information about weaknesses in Microsoft software.
He said the swift circulation of vulnerabilities alerted vandals and malicious hackers to their existence, and fostered attempts to exploit the loopholes.
Many said the desire to limit who gets to know about security problems was simply an attempt by the corporation to stifle bad news.
"Microsoft treats security vulnerabilities as public relations problems" said respected security researcher Bruce Schneier in a recent edition of his widely-read Crypto-Gram newsletter.
He said Microsoft should be more open about its products, especially as most of the loopholes are discovered by independent researchers.
Mr Schneier cited a study by Megan Carney at the University of Minnesota which showed that barely 10% of the software vulnerabilities reported to the Computer Emergency Response Team in 2001 were discovered by the makers of a program.
As an example, a recent article in the self-styled hacker quarterly 2600 declared that compromising Passport, Microsoft's method of identifying .Net users, was "easy to accomplish".
Alex Shipp, senior anti-virus technologist at MessageLabs, said he doubted Microsoft's conversion to the cause of good security would make much difference because so much of its software was already in circulation.
"We have seen things getting worse every year," he said.
Microsoft faced more problems than most because its software was complex, widely used, often poorly administered and was regularly targeted by both malicious hackers and virus makers, said Mr Shipp.
"The virus writers always go for the things that spread their virus best," he said. "They target Microsoft because it is so successful."