The world's largest software maker caught investors off guard last week when it said it would sacrifice billions of dollars in profit next year to invest in new business areas. Investors complained about the lack of clarity in Microsoft's plans to compete with online rivals Google and Yahoo.
Speaking at an event to promote Microsoft's online advertising efforts, Mr Ballmer said investments in the coming fiscal year, starting July 1, are a sign of Microsoft's commitment to be a leader on the web.
"These are certainly early days in this internet world. I believe only two or three companies can really deliver the infrastructure that's required to keep pace with both consumer demand and advertisers' needs," he said.