EVERY day for up to ten minutes near the London Stock Exchange, someone blocks signals from the global positioning system (GPS) network of satellites. Navigation systems in cars stop working and timestamps on trades made in financial institutions can be affected. The incidents are not a cyber-attack by a foreign power, though. The most likely culprit, according to Charles Curry, whose firm Chronos Technology covertly monitors such events, is a delivery driver dodging his bosses’ attempts to track him.
The signals are weak. Mr Curry likens them to a 20-watt light bulb viewed from 12,000 miles (19,300 km). And the jammers are cheap: a driver can buy a dashboard model for about £50 ($78). They are a growing menace. The bubbles of electromagnetic noise they create interfere with legitimate GPS users. They can disrupt civil aviation and kill mobile-phone signals, too. In America their sale and use is banned. In Britain they are illegal for civilians to use deliberately, but not, yet, to buy: Ofcom, a regulator, is mulling a ban. In recent years Australian officials have destroyed hundreds of jammers.