Thousands of visitors have fond memories of the medieval Czech capital Prague, with one exception: getting ripped off by a taxi driver.

But a Czech firm, Et netera, said on Tuesday it had developed a weapon to eradicate the long-lasting problem, a mobile phone application using the global positioning system that measures the distance and calculates the proper fare.

"Everyone will be able to verify right in the taxi whether the driver is trying to rob him," the company said in a statement introducing the service, called "virtual meter."

Some dishonest drivers have been using "turbo" meters charging illegal higher fares, taking passengers via the longest possible routes, refusing to produce receipts, and there has even been a case of a driver who had wired up the seats so he could deliver an electric shock to any troublesome passengers.

The city of Prague has for years fought to clean up the taxi service, with some success, but hailing down an unknown cab on the street is still risky. Several years ago, the Prague mayor was himself overcharged during an inspection ride.

Et netera said it was offering its system to the city, with the capability to directly report dishonest drivers to the regulator. Downloading the application should be free.

The firm said it decided to offer the system to city hall after one of its foreign business partners fell prey to an overcharging driver.