Exports of crude from the Kozmino oil terminal on Russia’s Pacific coast have become harder to track in recent days, after ships’ automated position signals began to suffer electronic interference.

The process, known as spoofing, sees signals sent between ships and the satellites used for global positioning systems swamped by false transmissions, which lead to vessels reporting themselves to be in impossible positions or moving at infeasible speeds.

Until early August, the issues had been confined largely to geopolitical hotspots like the Persian Gulf, the Strait of Hormuz and the Red Sea. They had also become much more common around Russia’s ports in the Black Sea, the Baltic and even the Arctic, ship-tracking data compiled by Bloomberg show.

But at Kozmino, which has become Moscow’s most important crude outlet, ship signals were largely free from interference. That has now changed. Tankers are showing up on hilltops, or traveling at impossible speeds in excess of 50 miles an hour.

The reason is unclear, especially given that the port is far from the war in Ukraine. It could be that Moscow has become concerned for Kozmino’s safety after Kyiv launched a daring attack using drones hidden in trucks, which targeted a military airfield in Russia’s Far East. It may also be related to a series of unexplained explosions on tankers in, or which had recently visited Russian ports. Or it could be a response to increased threats to the buyers of Russian oil, particularly those in India.

Whatever the reason, the tracking of exports from Kozmino just got a lot more complicated.