Scammers are extracting money from unsuspecting customers after tampering with ticket machines to ensure that any notes inserted become trapped in the machine, Zurich police told new agency ATS on Friday.
Once the customer sees the error message on the screen and goes off to get help from station staff, the scammers step in and extract the money from the machine.
Since the beginning of September police have recorded around 30 cases of the ‘Marseille trap', so-called because it was first seen in the French city.
Police are advising anyone receiving an error message on a ticket machine to stay by the machine and send someone else to seek help.
Customers should also inform the police should they see anyone acting suspiciously around ticket machines.