Borgaonkar informed Google of the vulnerability in June, he said. A fix was issued quickly, he said, but it was not publicized, leaving smartphone owners largely unaware that the problem existed and how they could fix it.
Google declined to comment. Android debuted in 2008 and now dominates the smartphone market. Nearly 198 million smartphones using Android were sold in the first six months of 2012, according to the research firm IDC. About 243 million Android-equipped phones were sold in 2011, IDC said.
Versions of Android that are vulnerable include Gingerbread, Ice Cream Sandwich and Jelly Bean, according to Borgaonkar. He said the Honeycomb version of Android, designed for tablets, needs to be tested to determine whether it is at risk, as well.
Samsung, which makes most of the Android phones, said only early production models of the Galaxy S III were affected and a software update has been issued for that model. The company said it is conducting an internal review to determine whether other devices are affected and what, if any, action is needed. Samsung said it is advising customers to check for software updates through the "Settings: About device: Software update" menu available on Samsung phones.
Borgaonkar, a researcher at Germany's Technical University Berlin, said the bug works by taking advantage of functions in phones that allow them to dial a telephone number directly from a web browser. That convenience comes with risk, however. A hacker, or anyone with ill intent, can create a website or an app with codes that instruct the phones linking to those numbers to execute commands automatically, such as a full factory reset.