Microsoft has secretly acquired 15 small companies in the last twelve months, Tech Flash reports.

The acquisitions have all been less than $75 million. Microsoft's managing director for business development Marc Brown says, "typically it will be 20 to 30 people who haven't yet begun to add the marketing muscle and haven't started to look internationally in terms of distribution and we find great people and great technology in that set of companies."

This is surprising news because CB Insights recently noted Microsoft has announced zero acquisitions this year.

When we wrote up CB Insight's report, we asked Microsoft if it was true that the company hadn't bought any companies. Microsoft chose not to comment.

Why is Microsoft being so silent? (As opposed to Google which seemingly announces every tiny pick up?)

One theory, which makes sense to us, from Joesph Tartakoff at paidContent: Microsoft doesn't want investors to think it's just freely spending money. The company is trying to be conservative.

Another idea: These acquisitions could be going into products Microsoft isn't ready to announce.