As Russian President Vladimir Putin and a convoy of construction vehicles rolled across one of the most controversial new bridges in the world on May 15, 2018, something funky began happening on ships anchored nearby in the Kerch Strait.

The ships' GPS systems suddenly began to indicate they were actually 65 kilometers away, on land, in the middle of an airport.

The incident is one of many highlighted in a new report that found the Kremlin "spoofed" global positioning systems, or GPS, to effectively place a bubble around Putin or properties associated with him. The researchers, with a nonprofit called C4ADS and the University of Texas at Austin, used public marine GPS databases, as well as a GPS monitoring device on the International Space Station to track similar instances.

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The yearlong study identified a pattern in which GPS devices near Putin and his entourage suddenly gave incorrect readings. The researchers also identified five buildings associated with the Kremlin that appeared to employ the technique on a rolling basis.

The researchers theorize that one reason "spoofing" is deployed is to protect Putin and other Russian officials from attacks or surveillance by drones that rely on GPS.

"The purpose of this spoofing activity was likely to prevent unauthorized civilian drone activity as a VIP protection measure," they wrote in the study.

However, there's a drawback to creating a GPS bubble around a world leader, said Todd Humphreys, an engineering professor at the University of Texas at Austin, who was involved with the study. It also makes it easier to keep track of Putin.

"What's ironic is if you look at these patterns, and if you coordinate it with the movements of the leader of Russia, it appears you have a Putin detector," Humphreys said. In other words, if you detect spoofing, there's a good chance Putin may be nearby.

The technique could also prove dangerous. The 24 maritime vessels that reported the Kerch bridge incident were otherwise unaffected. But Humphreys said a similar tactic in Syria could affect airplanes, which require functioning GPS to stay out of harm's way.

The researchers identified Russian equipment in Syria emitting what Humphreys described as "a whole different signal, one that was much much stronger, but not spoofing." The signal appeared to be jamming airplane GPS units, effectively rendering their navigation systems inoperable.

When the same tactic was apparently deployed during large-scale Russian military exercises in eastern Europe, civilians saw the effects, according to the report.

"Norway and Finland reported severe GPS outages affecting commercial airliners and cell phone networks for several days," according to the report.

Humphreys said the U.S. government has similar capabilities, but when deploying or testing spoofing or jamming equipment, it typically notifies mariners and airmen.