"Android's success has yielded ... a hostile, organized campaign against Android by Microsoft, Oracle, Apple and other companies, waged through bogus patents," wrote David Drummond, Google's chief legal officer, in a blog post on the company's Web site.

Drummond bristled about moves by major firms to "band together" to acquire patents held by struggling firms, citing a successful and others in June to acquire 600 patents from Nortel.

He suggested Microsoft and Apple may contend that Android infringes on these "dubious" patents, forcing Google to pay damages or license fees that would raise the costs of smartphones.

"Patents were meant to encourage innovation, but lately they are being used as a weapon to stop it," Drummond wrote. "Instead of competing by building new features or device, [competitors] are fighting through litigation."

Florian Mueller, an observer who has posted blogs about numerous Android patent disputes, has criticized Google for not rising to the defense of Android and its large, global group of independent developers.