Allison Nixon had helped arrest dozens of members of The Com — a loose affiliation of online groups responsible for violence and hacking campaigns. Then she became a target.

A researcher, professor and federal policy adviser, he guided students who went on to do groundbreaking work in connecting the world online.

Ham radio operators may be familiar with slow-scan television (SSTV) where an image is sent out over the airwaves to be received, decoded, and displayed on a computer monitor by other radio ...