Far from letting Microsoft run off with DoubleClick, Google has now entered the bidding process, reports CNET.

Previous reports had Microsoft as the frontrunner for acquiring the ad server. While Microsoft is still in contention, the rising asking price - now over $2 billion - may be out of Microsoft's league. Google's entry into the acquisition talks is likely to drive the final price higher.

Yahoo and AOL have talked with DoubleClick recently, though it's not known whether AOL is still an active contender.

Private equity firm Hellman & Friedman bought DoubleClick less than two years ago for $1.1 billion.