The invention relates to a self service terminal, such as an Automated Teller Machine, comprising a front panel provided with a card insertion slot for inserting a magnetic card therethrough, wherein, during insertion through the insertion slot, a magnetic stripe on the card induces a card data flux into a stripe data reading zone. The terminal also comprises an anti-skimming unit for generating a jamming field so as to jam a magnetic recording unit of an illegal card reader installed near or in the card insertion slot of the front panel. The anti-skimming unit includes a first magnetic field source and at least one further magnetic field source, each source inducing a electro-magnetic field in a slot region including the card insertion slot, such that the jamming field in the stripe date reading zone deviates from the jamming field outside the stripe data reading zone.