December 2019: Researchers at the Center for Advanced Defense Studies (C4ADS), a nonprofit that analyzes global conflict and security issues, have published evidence suggesting that GPS signal spoofing is behind maritime AIS (automatic identification system) disruptions in Shanghai. Data aggregated over many weeks showed ship locations appearing at different locations in large "rings: on the eastern bank of the Huangpu river.

At the ION GNSS+ conference in September, Dr. Humphreys showed a visualization of the data.

“To be able to spoof multiple ships simultaneously into a circle is extraordinary technology. It looks like magic,” he said. Attendees at the conference began to refer to the mysterious patterns as "crop circles."

Read the full article featuring Dr. Humphreys in the MIT Technology Review to learn what some experts think might be the reason for the mystery spoofing.