A company researching the security of smartphones has found a way of exploiting the differences in how humans and machines recognize speech in order to hijack a smartphone. To a human the instruction sounds like noise and can be hidden in other broadcasts so that a human would not recognize it as speech but think it was background noise. But to a smartphone it sounds like an instruction to open the browser and go to a website which is compromised in some way or to allow some other exploit. They say the attack is unlikely in the wild and difficult to execute, but recommend turning off non-authenticated voice control anyway.

http://www.bbc.co.uk/news/technology-36763902