Microsoft turned up the heat on Tuesday in its technological rivalry with Google as it announced the purchase of a private Silicon Valley company that has developed one of the most promising, and controversial, new internet search tools of recent years.

The acquisition of Powerset, reportedly for about $100m, comes in the wake of Microsoft’s failure to challenge Google either by acquiring Yahoo outright or buying its internet search business, although the software company has said that the offer of a partial purchase remains open.