The past year has seen Google increasingly becoming a rival of Apple. The competition between the two companies have been growing with the intrusion of Google into fields ruled by Apple. It began with Android and expanded through Google Chrome and Chrome OS. This led to the resignation of Google CEO Eric Schmidt from Apple’s Board of Directors. Now with the release of the new Google Phone (Nexus One), the two companies have become direct competitors.

It looks like Apple has finally decided to fight back by entering Google’s arena with the acquisition of the mobile ad company Quattro. Google had recently acquired AdMob, a four year old ad network, which had risen to be one of the most important players in the Mobile Ad industry. The deal is under scrutiny by the U.S. regulators. There were rumors that Apple also wanted to buy AdMob, but was out-bidden by Google.

The acquisition also puts Apple in direct competition with other companies like Microsoft and Yahoo.