I remember that a few years ago at a conference Richard Stallman asked one of the people in the room to turn off his cell phone because he did not want to be expected. If they look for videos of their talks on YouTube, they will see that they regularly touch on the subject saying that they can listen to our conversations from cell phones, even when they are turned off.
Is what he says true? While reading this, if you are not doing it from your mobile, you will probably have it half a meter away, so as a Spanish device it is perfect. We take them with us everywhere and nowadays it is normal that they are connected to the internet all the time and even with GPS activated.
Update: I published a new article where you can see how to infect Android with a Trojan and control it remotely. You can see it here Infecting and controlling Android from the computer.
The microphone can be activated remotely to listen to the ambient sound or record it, it is not something that the operating system allows to do by default, but there are applications that do it. One of them was discussed the other day in the article about the WhatsApp conversations, although StealthGenie is no longer operational.He was a Trojan that was initially promoted as a parental control tool and later directly as a Spanish application.
Once installed on the victim's cell phone, allow them to see the photos, videos, messages, calls and all the activity of the device, including activating the microphone to record the sound of the environment. All this working in a hidden way, in the following video you can see its operation from minute 9, it is a series of demonstrations that Chema Alonso did some time ago for a TV program (I recommend watching it in full):
There are many other similar applications and the good thing for users is that most are detected and blocked by mobile antivirus, although if the attacker is a person from the immediate environment with access to the device, the antivirus may not be as effective.
One of those that has become fashionable for Android is the one that can be seen in the following image. This will be the control panel on the PC from which you can spy on or control the phones that have the Trojan, the name I will not publish for obvious reasons:
One of the features allows you to activate the microphone to listen to the ambient sound in real time and also record it:
As you can see its use is very simple and intuitive, to the point that it can be used by all kinds of users. In other words, Stallman is right, although he points to another level like governments and manufacturers of proprietary software, spying through the microphone is possible.
Now, for this or another similar Trojan to end up on your mobile, it is necessary that you install it manually or that you do it without knowing it when you download an application of dubious origin, such as a pirated version of Angry Birds or something like that. So you have to be very careful with the applications that are installed and in which hands the device is left.