HOWEVER much technology knows about you – and you would be surprised how much it does (see "I exposed how firms and politicians can manipulate us online") – there is one firewall that it can't penetrate: your skull. Unless you choose to share your thoughts, they remain private. Increasingly, a combination of brain scanning and artificial intelligence is opening the black box, gathering signals from deep inside the mind and reverse-engineering them to recreate thoughts. For now, the technology is limited to vision – working out what somebody is looking at from their brain activity (see "Mind-reading AI uses brain scans to guess what you're looking at") – but in principle there appears no reason why the entire contents of our minds couldn't be revealed. This line of research inevitably raises fears about the ultimate invasion of privacy: mind reading.