It's very simple to interfere with GPS signals.

According to the Economist, near the London Stock Exchange, someone would block the GPS signal for up to ten minutes every day. As a result, the car navigation system stopped working and the transaction timestamp was also affected.

This accident was not a cyber attack launched by some foreign force, but very likely a delivery driver used GPS jamming tool to avoid being tracked by his boss. GPS jammers are very cheap, costing only tens of dollars, while GPS signals are very weak, equivalent to looking at the light emitted from a 20-watt bulb from 19,000 kilometers away.

In the United States, it is illegal to use and sell GPS jammers; in the UK, it is illegal to deliberately use GPS jammers, but there is no ban on purchases. The regulatory authority is considering issuing a ban. In the wrong hands, the jammer can become a weapon. For example, North Korea has used large-scale GPS jammers to block GPS signals in South Korea. In 2012, North Korea caused GPS interruptions for 1016 aircraft and 254 ships over a period of 16 days.