From January, Internet Explorer (IE) users will be automatically updated to the latest version of the browser.
Microsoft said it was starting the project to update millions of machines to improve security online.
Future updates to the browser would be applied without a user's knowledge to help beat scammers catching people out with fake updates.
Those who did not want their browser updated could opt out or uninstall the software, said Microsoft.
"The Web overall is better - and safer - when more people run the most up-to-date browser," wrote Ryan Gavin, Microsoft's IE boss, in a blogpost explaining the plan.
He said the data gathered by Microsoft for its security intelligence reports showed that many cyber criminals targeted old or outdated software when they tried to trick people into installing fake updates.
To beat such scams, Mr Gavin, said that once the latest version of the browser was installed all future updates would arrive silently and be applied without a user getting involved.
Chester Wisniewski, senior security advisor at Sophos, said the plan would aid those who did not see the importance of staying up to date.
"Microsoft has been struggling with browser stragglers for years," he said in a statement.Demise of IE6
The giant upgrade programme will affect IE users running Windows XP, Vista and 7, and will first be rolled out in Australia and Brazil. Only those Windows users with automatic updates turned on will be enrolled in the programme.
Those using Windows XP will be upgraded to IE8, while those on Vista and 7 get bumped up to IE9. This will probably mean the demise of IE6, a 10-year-old version of the browser that Microsoft has been trying to kill off for a while.
Figures gathered by Microsoft suggest IE6 is used by about 8.3% of people around the world, with the biggest number of users in China, where almost 28% of people remain wedded to it.
Globally, Internet Explorer is still the most popular browser, with more than 52% of people using it, according to net market research firm Net Applications. Mozilla's Firefox and Google's Chrome are battling it out for second place.
Microsoft said it had made tools that would let people avoid or uninstall the more up-to-date versions of the browsers if they wanted to stay with an older copy.