Android has been beset with legal challenges from all sides, including a , and complaints brought by Apple against Android device makers including HTC and Samsung. Meanwhile, Microsoft has been , saying it owns technology patents related to Google's mobile OS.

The Motorola acquisition, , should help shield Google and its partners from future legal action by Apple and others. But it may be too late to help device makers facing lawsuits already under way, and it won't help Google to fight Oracle's Java patent infringement lawsuit, which is due to begin trial in October, legal experts said.

Google never put much value in building its own patent portfolio and was caught off guard by the "patent arms race" that has come to define the wireless industry. Last week it , accusing Microsoft, Apple and others of trying to impose a "patent tax" on Android to stifle its runaway growth.

So its announcement Monday that it will pay $40 per share for Motorola -- or 63 percent over Friday's closing stock price -- came as little surprise to some observers. The acquisition will "increase competition by strengthening Google's patent portfolio, which will enable us to better protect Android from anti-competitive threats from Microsoft, Apple and other companies," CEO Larry Page said in a .

Alexander Poltorak, chairman and CEO of General Patent Corp., said Motorola's portfolio will serve as a deterrent to companies thinking of suing Google or its partners. "Now they will think twice before filing a complaint, because they can be guaranteed Google will strike back," he said.