Purchase of Right Media online ad exchange raises stakes after rival Google's recent buy of online ad firm DoubleClick.

After Google's acquisition of DoubleClick, it was widely assumed that many smaller online advertising firms were "in play". The fact that Microsoft was also a DoubleClick suitor combined with the fact that Google's rivals couldn't afford to fall too far behind meant it was only a matter of time before another deal was made. Hoping to provide an alternative to the growing Google behemoth, Yahoo has announced the purchase of privately held Right Media, a company in which it already has a 20% stake. Yahoo says that it will create an open ad marketplace, which sounds a lot like the idea that DoubleClick had cooking up before the Google purchase was announced. This isn't likely to be the last deal. Microsoft's Steve Ballmer recently said that his biggest regret was that the company has come late to the online advertising game, which suggests that the company will probably make a deal to play catch up. Now that its two chief rivals have made these purchases, the pressure on Microsoft to get a similar deal done has been ratcheted up.