Why did Google buy Motorola? To fight back against the Apple and Microsoft’s multiple legal challenges currently raining down on its Android mobile operating system, says one of the company’s co-founders.

Larry Page explained that buying ailing mobile maker Motorola was a move to protect Android from patent lawsuits by both Microsoft and Apple – which he said “are banding together in anti-competitive patent attacks on Android”.

“We recently explained how companies including Microsoft and Apple are banding together in anti-competitive patent attacks on Android,” he said in a company statement today.

“The US Department of Justice had to intervene in the results of one recent patent auction to ‘protect competition and innovation in the open source software community’ and it is currently looking into the results of the Nortel auction.

“Our acquisition of Motorola 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.

David Drummond, Google’s Senior Vice President and Chief Legal Officer, had recently complained that Apple and Microsoft were ganging up on Google’s Android: “Microsoft and Apple have always been at each other’s throats, so when they get into bed together you have to start wondering what's going on.”

“Android’s success has yielded something else: a hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents.

“They’re doing this by banding together to acquire Novell’s old patents (the “CPTN” group including Microsoft and Apple) and Nortel’s old patents (the “Rockstar” group including Microsoft and Apple), to make sure Google didn’t get them; seeking $15 licensing fees for every Android device; attempting to make it more expensive for phone manufacturers to license Android (which we provide free of charge) than Windows Phone 7; and even suing Barnes & Noble, HTC, Motorola, and Samsung.

“Patents were meant to encourage innovation, but lately they are being used as a weapon to stop it.”

Samsung heads back to court on August 25 to defend its right to sell the Android-based Galaxy Tab 10.1 in Europe, following a preliminary injunction Apple obtained earlier last week at a German court.

In the complaint Apple accuses Samsung of giving up on product R&D and simply copying its iPad tablet: "Instead of pursuing independent product development, Samsung has chosen to slavishly copy Apple's innovative technology, distinctive user interfaces, and elegant and distinctive product and packaging design, in violation of Apple's valuable intellectual property rights".