Researchers have developed a technology to invisibly transmit information disguised as background thermal radiation. Using a phenomenon called “negative light,” they transferred 100 kilobits of data per second in a way that was completely undetectable to outside observers.

Most methods for concealing data during transfer involve hiding it among other data or encrypting it in a way that makes it impossible to read without a cipher or other means of decryption. The new technique, by contrast, makes the data almost impossible to intercept because there’s no indication it’s being sent at all. It can also be encrypted through traditional means to further harden security, the team wrote in a paper published March 5 in the journal Light: Science & Applications.