Scientists have discovered that optical signals from LED lights on electronics equipment can be captured from a distance using a telescope to reveal transmitted data. An expert demonstrated being able to collect strong signals from about 22 yards away. LED lights act as free-space optical transmitters, allowing eavesdropping on computer networks from outside buildings. While not all devices are vulnerable, some types of networks like ATM machines are at risk if equipment is visible from outside through windows. Covering LED lights or moving equipment away from windows can help prevent this type of spying.