The new version of IE, which will be released for preliminary testing this summer, will have new protections against viruses, spyware and "phishing" scams, which fool users into entering sensitive information on Web pages that appear to be legitimate.

Gates said security remains the biggest threat to the "fantastic advances" happening in the world of technology, and that Microsoft was spending more than a third of its annual $6 billion in research and development spending on security.

The move comes three years after Microsoft, the world's biggest software company, launched a major initiative to improve the reliability and security of its software, which runs on about 90 percent of all personal computers.