Steve Ballmer, Microsoft’s chief executive officer, on Thursday made his case to Wall Street for Microsoft to make big new investments in the internet business, in spite of signs of internal upheaval in the wake of his failed bid for Yahoo this year.

Mr Ballmer’s comments, which included his starkest warning yet that Microsoft would remain in “investment mode” indefinitely, or at least until it made a bigger dent in search and online advertising, came the day after the unexpected departure of the executive who ran the company’s online services business.