Microsoft wants to buy New York-based online advertising firm DoubleClick, according to the Wall Street Journal.

DoubleClick, which is majority-owned by private equity firm Hellman and Friedman, is said to be exploring options and working closely with Morgan Stanley to secure a possible sale with Microsoft.

A $2bn price tag has been placed on DoubleClick by the private equity firm. DoubleClick, which was founded in 1996 and went private in 2005, has seen revenue of $150m in the last year.

But what's in it for Microsoft? Surely the company could find a cheaper way to build or buy some ad-serving software. And paying $2bn to replace Atlas GMT, Microsoft's current ad-serving software of choice, for an inhouse service looks somewhat eccentric.

Which means that Microsoft would be paying a big premium to extend hooks into ad agencies and publishers, giving it some more heft in its struggle against the Google behemoth. ®