Abstract:
A method of preventing fraud at a self-service terminal is described. The method comprises: receiving a signal from an electromagnetic sensor located in the vicinity of an electromagnetic signal transmitter; monitoring a drive signal being delivered to the electromagnetic signal transmitter; and comparing the drive signal with the electromagnetic sensor signal. The method then ascertains if a state of the electromagnetic sensor signal is inconsistent with a state of the drive signal; and triggers an alarm when the state of the electromagnetic sensor signal is inconsistent with a state of the drive signal.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to fraud prevention. In particular, although not exclusively, the invention relates to preventing unauthorized reading of data from a card. 
       BACKGROUND OF INVENTION 
       [0002]    Unauthorized reading of card data, such as data encoded on a magnetic stripe card, while the card is being used (hereafter “card skimming”), is a known type of fraud. Card skimming is typically perpetrated by adding a magnetic read head (hereafter “alien reader”) to a fascia of an automated teller machine (ATM) to read a magnetic stripe on a customer&#39;s card as the customer inserts or (more commonly) retrieves the card from an ATM. The customer&#39;s personal identification number (PIN) is also ascertained when the customer uses the ATM. Examples of how this is achieved include: a video camera that captures images of the PINpad on the ATM, a false PINpad overlay that captures the customer&#39;s PIN, or a third party watching the customer (“shoulder surfing”) as he/she enters his/her PIN. The third party can then create a card using the card data read by the alien reader, and can withdraw funds from the customer&#39;s account using the created card and the customer&#39;s PIN (ascertained by one of the ways described above). 
         [0003]    Various methods have been proposed to defeat this type of fraud. One method involves transmitting an electromagnetic signal (hereafter a “jamming signal”) when the card is being transported so that the alien reader cannot detect the magnetically encoded data because of the presence of the jamming signal. Although this technique can be effective, it is possible to shield this jamming signal so that it does not interfere with the alien reader. 
       SUMMARY OF INVENTION 
       [0004]    Accordingly, the invention generally provides methods, systems, apparatus, and software for providing improved fraud prevention by detecting a lack of correlation between a magnetic sensor signal and a drive signal used to energize an electromagnetic signal transmitter. 
         [0005]    In addition to the Summary of Invention provided above and the subject matter disclosed below in the Detailed Description, the following paragraphs of this section are intended to provide further basis for alternative claim language for possible use during prosecution of this application, if required. If this application is granted, some aspects may relate to claims added during prosecution of this application, other aspects may relate to claims deleted during prosecution, other aspects may relate to subject matter never claimed. Furthermore, the various aspects detailed hereinafter are independent of each other, except where stated otherwise. Any claim corresponding to one aspect should not be construed as incorporating any element or feature of the other aspects unless explicitly stated in that claim. 
         [0006]    According to a first aspect there is provided a method of preventing fraud at a self-service terminal, the method comprising: 
         [0007]    receiving a signal from an electromagnetic sensor located in the vicinity of an electromagnetic signal transmitter; 
         [0008]    monitoring a drive signal being delivered to the electromagnetic signal transmitter; 
         [0009]    comparing the drive signal with the electromagnetic sensor signal; 
         [0010]    ascertaining if a state of the electromagnetic sensor signal is inconsistent with a state of the drive signal; and 
         [0011]    triggering an alarm when the state of the electromagnetic sensor signal is inconsistent with a state of the drive signal. 
         [0012]    The step of ascertaining if a state of the electromagnetic sensor signal is inconsistent with a state of the drive signal may include the sub-steps of: (i) ascertaining when the drive signal is activated and (ii) ascertaining the state of the electromagnetic sensor signal when the drive signal is activated. 
         [0013]    The step of triggering an alarm when the state of the electromagnetic sensor signal is inconsistent with a state of the drive signal may include: triggering an alarm if the electromagnetic sensor signal is already active at the moment the drive signal is activated. 
         [0014]    The step of ascertaining if a state of the electromagnetic sensor signal is inconsistent with a state of the drive signal may include the sub-steps of: (i) ascertaining when the drive signal is de-activated and (ii) ascertaining the state of the electromagnetic sensor signal when the drive signal is de-activated. 
         [0015]    The step of triggering an alarm when the state of the electromagnetic sensor signal is inconsistent with a state of the drive signal may include: triggering an alarm if the electromagnetic sensor signal is already inactive at the moment the drive signal is de-activated. 
         [0016]    According to a second aspect there is provided a fraud prevention device for use in a self-service terminal, the device comprising: 
         [0017]    an electromagnetic signal transmitter for emitting a jamming signal operable to interfere with any alien reader located near the electromagnetic signal transmitter; 
         [0018]    an electromagnetic sensor located in the vicinity of the electromagnetic signal transmitter and operable to detect the jamming signal; 
         [0019]    a signal generator operable to create a drive signal for driving the electromagnetic signal transmitter; 
         [0020]    a comparator operable to compare the drive signal with the electromagnetic sensor signal; and 
         [0021]    an alarm generator operable to trigger an alarm when the electromagnetic sensor signal is inconsistent with the drive signal. 
         [0022]    The signal generator, the comparator, and the alarm generator may be located on an external controller. 
         [0023]    The electromagnetic signal transmitter may comprise a plurality of coil drives. Each coil drive may be an inductive coil drive. 
         [0024]    The signal generator may include an inductive coil drive circuit operable to create a signal for each inductive coil drive, each signal having a fixed frequency. Each fixed frequency may be a frequency selected from the range of approximately one hundred hertz to ten kilohertz (100 Hz to 10 kHz). In one embodiment, the fixed frequency may be 2 kHz. 
         [0025]    The signal generator may also include a random signal generator circuit to create a first random signal for superimposing on the fixed frequency to excite the first inductive coil drive, and to create a second (different) random signal for superimposing on the fixed frequency to excite the second inductive coil drive. 
         [0026]    According to a third aspect there is provided a self-service terminal (SST) comprising: 
         [0027]    a card reader operable to detect presentation of a card; 
         [0028]    a fraud prevention device according to the second aspect. 
         [0029]    The self-service terminal may further comprise a proximity sensor operable to detect a customer&#39;s card while the card is presented by the customer. 
         [0030]    The proximity sensor may also be located within a card reader guide. 
         [0031]    The self-service terminal may be an automated teller machine (ATM), an information kiosk, a financial services centre, a bill payment kiosk, a lottery kiosk, a postal services machine, a check-in and/or check-out terminal such as those used in the retail, hotel, car rental, gaming, healthcare, and airline industries, and the like. 
         [0032]    For clarity and simplicity of description, not all combinations of elements provided in the aspects recited above have been set forth expressly. Notwithstanding this, the skilled person will directly and unambiguously recognize that unless it is not technically possible, or it is explicitly stated to the contrary, the consistory clauses referring to one aspect are intended to apply mutatis mutandis as optional features of every other aspect to which those consistory clauses could possibly relate. 
         [0033]    These and other aspects will be apparent from the following specific description, given by way of example, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a pictorial diagram of a rear perspective view of a card reader guide for use in a self-service terminal (SST) according to one embodiment of the present invention; 
           [0035]      FIG. 2  is an exploded pictorial diagram illustrating components of the card reader guide of  FIG. 1 ; 
           [0036]      FIG. 3  is a front perspective view of one part (the card reader guide cover) of the card reader guide of  FIG. 1 ; 
           [0037]      FIG. 4  is a rear perspective view of the card reader guide cover of  FIG. 3 ; 
           [0038]      FIG. 5  is a pictorial plan view of part (the magnetic reader detector) of one of the components of the card reader guide shown in  FIG. 2 ; 
           [0039]      FIG. 6  is a pictorial perspective view of the card reader guide of  FIG. 1 , with the card reader guide cover of  FIG. 3  shown as partially transparent to reveal the magnetic reader detector of  FIG. 5  located therein; 
           [0040]      FIG. 7  is a pictorial plan view of another part (the signal generator) of one of the components of the card reader guide shown in  FIG. 2 ; 
           [0041]      FIG. 8  is a pictorial perspective view of the signal generator of  FIG. 7 ; 
           [0042]      FIG. 9  is a simplified schematic view of a fascia of the SST incorporating the card reader guide of  FIG. 1  and illustrating an SST controller operable to control the SST; 
           [0043]      FIG. 10  is a block diagram of a detector controller for controlling the operation of the magnetic reader detector of  FIG. 5  and the signal generator of  FIG. 7 ; 
           [0044]      FIG. 11  is a graph illustrating a signal from the magnetic reader detector of 
           [0045]      FIG. 5  while a customer&#39;s hand is present in the vicinity of the card reader guide of  FIG. 1  to insert and then remove a card; and 
           [0046]      FIG. 12  is a flowchart illustrating the operation of software components executing on the SST controller of  FIG. 9 . 
       
    
    
       [0047]    It should be appreciated that some of the drawings provided are based on computer renderings from which actual physical embodiments can be produced. As such, some of these drawings contain details that are not essential for an understanding of these embodiments but will convey useful information to one of skill in the art. Therefore, not all parts shown in the drawings will be referenced specifically. Furthermore, to aid clarity and to avoid numerous leader lines from cluttering the drawings, not all reference numerals will be shown in all of the drawings. In addition, some of the features are removed from some views to further aid clarity. 
       DETAILED DESCRIPTION 
       [0048]    Reference is first made to  FIG. 1 , which is a pictorial diagram of a rear perspective view of a card reader guide  10  according to one embodiment of the present invention. The card reader guide  10  comprises a card reader guide cover  12  defining three apertured tabs  14  by which the card reader guide cover  12  is coupled to a rear part of a fascia (not shown in  FIG. 1 ) of an SST. 
         [0049]    The card reader guide  10  further comprises a shielding plate  20  coupled to the card reader guide cover  12  by three screws  22   a,b,c.    
         [0050]    Reference is now also made to  FIG. 2 , which is an exploded pictorial diagram illustrating components of the card reader guide  10 .  FIG. 2  illustrates a proximity detector  30  in the form of a magnetic reader detector and a signal generator  40  for creating a jamming signal.  FIG. 2  also shows a data card  42  (in the form of a magnetic stripe card) aligned with the card reader guide  10 . 
         [0051]    The card reader guide  10  is operable to receive the magnetic stripe card  42 , which is inserted by a customer. A magnetic stripe card has a large planar area (the length and width) on each of two opposing sides and a four thin edges therebetween. Two of these edges (front and rear)  43   a,b  are narrower than the other two edges (the side edges)  44   a,b . The magnetic stripe side (the lower side) of a card refers to the large planar area that carries a magnetic stripe  45  (shown in broken line in  FIG. 2 ). The magnetic stripe  45  is disposed parallel to the side edges  44   a,b.    
         [0052]    Opposite the magnetic stripe side (the upper side  47 ) there is a large planar area that (typically) does not carry a magnetic stripe  45 , but typically includes account and customer information embossed thereon. On some cards, the upper side  47  may carry integrated circuit contacts. On the magnetic stripe side of the card, the magnetic stripe  45  is not centrally located; rather, it is located nearer to one of the side edges (referred to as the magnetic stripe edge  44   a ) than to the other side edge (referred to as the non-magnetic stripe edge  44   b ). 
         [0053]    Reference will now also be made to  FIGS. 3 and 4 , which are front and rear perspective views, respectively, of the card reader guide cover  12 . 
         [0054]    The card reader guide cover  12  comprises a moulded plastics part dimensioned to be accommodated within, and partially protrude through, an aperture in a fascia (not shown). 
         [0055]    The card reader guide  10  defines a card slot  50  extending generally horizontally across the guide  10  in the direction of centre line  52 , from a non-stripe end  54  to a stripe end  56 . When the magnetic stripe card  42  is correctly inserted into the card slot  50  by a customer then the magnetic stripe  45  on the magnetic stripe card  42  is located closer to the stripe end  56  than to the non-stripe end  54 . 
         [0056]    The card reader guide  10  defines a breakout line  58  extending generally vertically (perpendicular to the card reader slot  50 ). The card reader guide  10  also defines a first (lower) protrusion  60 . 
         [0057]    The first (lower) protrusion  60  includes a planar section  62  across which the magnetic stripe side of a card passes as the card  42  is inserted. The first (lower) protrusion  60  also includes an upright section  64  that extends from the breakout line  58  to an end surface  66 . The end surface  66  is spaced from the card slot  50  to ensure that card does not protrude beyond the end surface  66  when ejected by a card reader (not shown) within the SST. 
         [0058]    A magnetic stripe path  68  is defined on the planar section  62 . This is the portion of the planar section  62  that the magnetic stripe  45  on a correctly inserted data card  42  will be in registration with when the card  42  is inserted or removed by a customer. In this embodiment, the magnetic stripe path  68  is centered on track two of a magnetic stripe. It is track two that carries the customer account information for the data card  42 , so track two is the track that alien readers attempt to read. 
         [0059]    The first protrusion  60  also defines a cavity (best seen in  FIG. 4  and shown generally by arrow  70 ), which is referred to herein as the “detector cavity”, and which is beneath the planar section  62  and within the card reader guide cover  12 . 
         [0060]    The card reader guide  10  defines a second (upper) protrusion  80  similar to, aligned with, and opposite the first protrusion  60 . 
         [0061]    The second (upper) protrusion  80  includes a planar section  82  (best seen in  FIG. 4 ) beneath which a magnetic stripe side of a card  42  passes as the card  42  is inserted. The second (upper) protrusion  80  also includes an upright section  84  that extends from the breakout line  58  to an end surface  86 . The second protrusion  80  defines a cavity  90  (referred to herein as the “signal generator cavity”) above the planar section  82  and within the card reader guide cover  12 . 
         [0062]    Referring again to  FIG. 2 , the magnetic reader detector  30  is dimensioned to be accommodated within the detector cavity  70  and is mounted therein by two screws  102  that engage with the card reader guide  10 . The magnetic reader detector  30  includes a communication cable  104  for routing signals and power between the magnetic reader detector  30  and an external controller (not shown in  FIG. 2 ). Such a controller would typically be located in an SST in which the card reader guide  10  is installed. 
         [0063]    Similarly, the signal generator  40  is dimensioned to be accommodated within the signal generator cavity  90  and is mounted therein by two screws  106  that engage with the card reader guide  10 . The signal generator  40  also includes an output cable  108  for routing signals and power between the signal generator  40  and the external controller (not shown in  FIG. 2 ). 
         [0064]    A drainage pipe  109  is also provided to drain away any water ingress from the card slot  50 . 
         [0065]    Reference will now be made to  FIG. 5 , which is a pictorial plan view of part of the magnetic reader detector  30 . The magnetic reader detector  30  comprises a track printed circuit board (pcb)  110  on which is disposed part of a capacitive sensor  112  and an electronic drive circuit (not shown) located beneath the track pcb  110 . 
         [0066]    The magnetic reader detector  30  is physically configured to conform to the shape of the detector cavity  70  so that when the magnetic reader detector  30  is inserted into the detector cavity  70  the track pcb  110  fits securely in place. 
         [0067]    The capacitive sensor  112  operates in a similar way to a capacitive proximity sensor, as will now be described. The capacitive sensor  112  comprises a transmit plate  114  separated from a receive plate  115  by a linear track (a ground strip)  116 . The transmit plate  114 , receive plate  115 , and ground strip  116  are all defined as conducting tracks on the track pcb  110 . 
         [0068]    The ground strip  116  is located on the track pcb  110  such that when the magnetic reader detector  30  is inserted into the lower protrusion  60  of the card reader guide  10 , the ground strip  116  is in registration with the magnetic stripe path  68 . In particular, the ground strip  116  is aligned with track two of the magnetic stripe path  68 . This is illustrated in  FIG. 6 , which is a pictorial perspective view of the card reader guide  10 , with the card reader guide cover  12  shown as partially transparent to reveal the magnetic reader detector  30 . 
         [0069]    The capacitive sensor  112  operates by transmitting an alternating signal on the transmit plate  114 , which creates an electric field between the transmit plate  114  and the receive plate  115  that arches over the ground strip  116 , the air gap in the arch providing the dielectric. If a material (such as an alien reader, or a data card) is inserted into this electric field then the dielectric changes, which changes the phase and magnitude of the electric field. This is detected by the receive plate  115 . 
         [0070]    Drive and signal processing circuitry (not shown) is located on a drive pcb  117  (located beneath the track pcb  110 , as shown in  FIG. 6 ) to provide the alternating signal and detect the phase and magnitude changes. 
         [0071]    The geometry, configuration, and location of the transmit plate  114 , receive plate  115 , and ground strip  116  optimizes the probability of the capacitive sensor  112  detecting an alien reader, because any alien reader must be located at a point over which track two of the card&#39;s magnetic stripe will pass, and the electric field is located along this path. 
         [0072]    The track pcb  110  also includes two magnetic signal sensors  118   a,b  mounted on an underside thereof. 
         [0073]    The communication cable  104  conveys one signal from each of the two magnetic sensors  118 , power to supply the capacitive sensor  112 , and one response signal from the capacitive sensor  112 . 
         [0074]    Reference will now be made to  FIGS. 7 and 8 , which are a pictorial plan view and perspective view respectively, of part of the signal generator  40  shown relative to the magnetic stripe path  68 . 
         [0075]    The signal generator  40  comprises a pair of inductive coil drives  120   a,b . Each inductive drive coil  120   a,b  comprises a generally C-shaped (when viewed from the side) ferrite core  122   a,b  having opposing poles (north pole  124   a,b  (only  124   a  is shown) and south pole  126   a,b ) at opposite ends, and being wound with wire  128   a,b  at a central portion. Each inductive coil drive  120   a,b  is driven by a signal from the external controller (not shown). The C-shape of the ferrite cores ensures that most of the electromagnetic field generated by the inductive coil drives  120   a,b  extends downwards towards the magnetic stripe path  68 , rather than upwards. 
         [0076]    Each of the inductive coil drives  120   a,b  straddles the magnetic stripe path  68  but the two inductive coil drives are longitudinally offset relative to each other (as shown in  FIG. 7 ). Thus, the two inductive coils  120   a,b  do not generate a symmetric electromagnetic field. This longitudinal offsetting makes it more difficult for a fraudster to filter out the combined signal from the two inductive coil drives  120   a,b.    
         [0077]    One of the two magnetic sensors  118   a,b  is in registration with a centre point between the poles  124   a , 126   a  of the first ferrite core  122   a , the other of the two magnetic sensors  118   b  is in registration with a centre point between the poles of the second ferrite core  122   b . Each of the two magnetic sensors  118   a,b  measures the magnetic signal present. If the two inductive coils  120   a,b  are active then a large magnetic signal should be detected by each of the two magnetic sensors  118   a,b.    
         [0078]    Reference will now also be made to  FIG. 9 , which is a pictorial diagram of a fascia  140  of an SST  150  that includes the card reader guide  10 , and shows the data card  42  partially inserted therein. 
         [0079]    A motorized card reader  170  (illustrated in broken line) is aligned with, and located behind, the card reader guide  10  so that a card transport path (not shown) in the card reader  170  aligns with the card slot  50  of the card reader guide  10 . The card reader  170  includes a card reader controller  172  for controlling operation of the card reader  170 . 
         [0080]    In this embodiment the motorized card reader is from Sankyo Seiki Mfg Ltd at 1-17-2, Shinbashi, Minato-Ku, Tokyo, 1058633, Japan. However, any other suitable motorized card reader could be used. 
         [0081]    The SST also includes an SST controller  174 , which includes a card guide control circuit  180  implemented as an expansion board that slots into a motherboard (not shown) on which a processor  182  is mounted. The processor  182  executes an SST control program  184 . 
         [0082]    The SST control program  184  controls the operation of the SST, including communicating with modules such as the card reader  170 , and presenting a sequence of screens to a customer to guide the customer through a transaction. 
         [0083]    Reference will now also be made to  FIG. 10 , which is a simplified block diagram of the card guide control circuit  180  that is used to control the electronic components in the card reader guide  10  and to indicate if an alien reader may be present. 
         [0084]    The control circuit  180  receives five inputs. Three of these inputs are fed into a detector  190 , the other two inputs are fed into a monitor  200 . 
         [0085]    One of the detector inputs (the width switch status)  202  comes from the card reader  170  and indicates the status of a width switch (not shown) on the card reader  170 . As is known in the art, when the width switch is closed, this indicates that an object inserted into the card reader  170  has a width that matches that of a standard data card. 
         [0086]    Another of the detector inputs (the shutter status)  204  indicates the status of a shutter (not shown) in the card reader  170 . The shutter can either be open or closed and controls access to a card reader path within the card reader  170 . 
         [0087]    The shutter  170  is only opened by the card reader controller  172  ( FIG. 9 ) within the card reader  170  if the width switch is closed and a magnetic pre-read head (not shown) in the card reader  170  detects a magnetic stripe. As is known in the art, the pre-read head is used to ensure that a data card has been inserted in the correct orientation. 
         [0088]    The third detector input (from the capacitive sensor  112 )  206  indicates the state of the output signal from the capacitive sensor  112 . The capacitive sensor input  206  indicates whether an object is present in the vicinity of the magnetic stripe path  68 . 
         [0089]    The two inputs  210 , 212  (referred to as magnetic signal inputs) that are fed into the monitor  200  are from the two magnetic sensors  118   a,b . These magnetic signal inputs  210 , 212  indicate the presence of an electromagnetic signal at each of the two magnetic sensors  118   a,b  respectively. 
         [0090]    The detector  190  includes logic circuitry (not shown in detail) and provides an active output  220  (referred to as the jam signal) when the width switch is open (the width switch status input  202  is active), the shutter is open (the shutter status input  204  is active), and an alien object is detected by the capacitive sensor input  206  (essentially this is a Boolean AND function). When this condition occurs, the control circuit  180  generates a jamming signal. This should occur every time a card is inserted by a customer because the inserted card changes the dielectric value of the air gap above the capacitive sensor  112 . 
         [0091]    The jam signal  220  is fed into a random number generator circuit  230  (which may generate truly random or pseudo random numbers). Random number generating circuits are well-known to those of skill in the art so will not be described herein in detail. 
         [0092]    The random number generator circuit  230  provides two outputs: a first random signal  232  and a second random signal  234 . These two outputs  232 , 234  (which convey different random signals) are fed into a coil driver circuit  240 . 
         [0093]    The coil driver circuit  240  generates two base signals (a first base signal and a second base signal), each centered on approximately  2 kHz. The coil driver circuit  240  applies the first random signal  232  to the first base signal; and the second random signal  234  to the second base signal, and outputs these as a first drive signal  242  and a second drive signal  244  respectively. In this embodiment, the random signals are in the form of a bit pattern sequence. The coil driver circuit  240  uses the random signals (the bit pattern sequences) to change the duty cycle of each of the first and second base signals. That is, the random signals are used to provide pulse width modulation of the  2 kHz signals. The important point is that the random signals  232 , 234  are used to impart some randomness to the regular ( 2 kHz) base signals. This randomness may comprise pulse width modulation, amplitude modulation, superimposing a high frequency component on a base signal, or any other convenient technique. This added randomness makes it much more difficult to filter out the signals. 
         [0094]    The first drive signal  242  is output to the first inductive coil drive  120   a ; and the second drive signal  244  is output to the second inductive coil drive  120   b . Thus, the first and second drive signals  242 , 244  are the signals that drive the inductive coil drives  120   a,b.    
         [0095]    The first and second drive signals  242 , 244  are also output to the monitor  200 . The main purpose of the monitor  200  is to ensure that the magnetic reader detector  30  is not being (i) jammed by an external signal, or (ii) screened so that it does not detect an alien reader. To achieve this purpose, the monitor  200  continually monitors the two magnetic signal inputs  210 , 212  from the two magnetic sensors  118   a,b . As mentioned above, these magnetic signal inputs  210 , 212  indicate the presence of electromagnetic signals at the two magnetic sensors  118   a,b.    
         [0096]    The monitor  200  correlates these two magnetic signal inputs  210 , 212  with the jam signal  220 . Due to time delays in creating an electro-magnetic field at the coil drives  120 , there will be a short delay between each of the coil drive signals  242 , 244  going active, and the two magnetic sensors  118   a,b  detecting an electro-magnetic field. Hence there will be a delay between the coil drive signals  242 , 244  going active and the magnetic signal inputs  210 , 212  going active. Similarly, when the coil drive signals  242 , 244  go inactive, there will be a short delay before the magnetic signal inputs  210 , 212  go inactive. 
         [0097]    If the monitor  200  detects that a magnetic signal input  210 , 212  is active at the instant when the associated coil drive signal  242 , 244  has just transitioned to active, then this may indicate that a third party is attempting to jam the magnetic reader detector  30 . This is because there should be a time delay between the coil drive signal  242 , 244  going active and an electro-magnetic field being detected. If there is no time delay, then the magnetic signal input  210 , 212  that was detected as active must have been active before the coil drive signal was activated. If such an event occurs on “m” consecutive occasions, then the monitor  200  activates a jam attack output  252 . The jam attack output  252  indicates that an electromagnetic field is present that was not generated by the coil drives  120   a,b . In this embodiment, “m” is four, so the jam attack output  252  is activated if this condition occurs on four consecutive occasions. 
         [0098]    Similarly, if the monitor  200  detects that a magnetic signal input  210 , 212  is inactive at the instant when the associated coil drive signal  242 , 244  has just transitioned to inactive, then this may indicate that a third party is attempting to shield (or screen) the magnetic reader detector  30  from the electromagnetic field generated by the coil drives  120   a,b . This is because there should be a time delay (a time lag) between the coil drive signal  242 , 244  going inactive and the electro-magnetic field generated by those coil drives  120   a,b  reducing to zero. If there is no time delay, then the magnetic signal input  210 , 212  that was detected as inactive must have been inactive before the coil drive signal was inactivated. If such an event occurs on “n” consecutive occasions, then the monitor  200  activates a weak output  254 . The weak attack output  254  indicates that no electromagnetic field is present even though the coil drives  120   a,b  are generating (or attempting to generate) an electromagnetic field. This may indicate that a third party is attempting to shield (or screen) the two inductive coil drives  120   a,b  to prevent them from jamming an alien reader. In this embodiment, “n” is four, so the weak output  254  is activated if this condition occurs on four consecutive occasions. 
         [0099]    If both of the magnetic sensors  118   a,b  detect magnetic signals that correlate with the first and second drive signals  242 , 244 , then the monitor  200  activates a normal (OK) output  256  to indicate that the correct jamming signals have been detected from the inductive coil drives  120   a,b . In other words, if both of the magnetic sensors  118   a,b  detect magnetic signals that are correctly offset from the first and second drive signals  242 , 244  respectively, then the monitor  200  activates the normal output  256 . In this embodiment, correctly offset means that there is a time delay between each of the magnetic sensors  118   a,b  and its associated first and second drive signal  242 , 244  that corresponds to an expected time delay. 
         [0100]    The card guide circuit  180  also includes a local processor  260  executing firmware  262 . The firmware  262  interfaces with the logic circuitry in the card guide circuit  180 , and communicates with the SST control program  184  via a USB interface  264 . 
         [0101]    The local processor  260  receives the three outputs  252 , 254 , 256  from the monitor  200  and also the jam signal  220 , and the firmware  262  decides whether to raise an alarm based on the status of these signals. 
         [0102]    The firmware  262  may transmit an alarm signal if the jam signal  220  is active for longer than a predetermined length of time, for example, one minute, or if either of the weak output  254  or the jam attack output  252  is active, or if either of the weak output  254  or the jam attack output  252  is active for longer than a predetermined time (for example, five seconds). 
         [0103]    The firmware  262  communicates with the SST control program  184  and provides an alarm signal (which may be active or inactive) thereto over the USB interface  264 . This enables the SST control program  184  to take action if the alarm signal is active. The firmware  262  may also include a simple network management protocol (SNMP) agent (not shown) that transmits a trap to a remote management centre (not shown) if the alarm signal is set active by the firmware  262 . 
         [0104]    During operation, when a customer inserts the data card  42 , the width switch is closed and the pre-read head detects the magnetic stripe  45  on the underside of the card  42 . The card reader  170  then opens the shutter. The capacitive sensor input  206  indicates that an object (the data card  42 ) is present. This combination causes the detector  190  to activate the jam signal  220 . 
         [0105]    The active jam signal  220  causes the random number generator  230  to generate the first and second random signals  232 , 234 , which the coil driver  240  applies to the first and second base signals to generate the first and second drive signals  242 , 244 , which now have different duty cycles. These signals  242 , 244  are used to power the inductive coil drives  120   a,b  respectively, which create electromagnetic fields around the data card  42 . In this embodiment, the random signals  232 , 234  are continuous bit streams that are applied to the base signals as the base signals are being generated. 
         [0106]    The monitor  200  attempts to correlate the two inputs  210 , 212  from the two magnetic sensors  118   a,b  with the first and second drive signals  242 , 244 . 
         [0107]    If the signals correlate (that is, the transitions are correct and occur at approximately the correct time delay) then the monitor  200  activates the normal (OK) output  256 . 
         [0108]    If when the first drive signal  242  goes active, the magnetic signal input  210  is already active, then the monitor  200  records this as a potential jam and increments a counter. If this occurs four times in succession, then the monitor  200  activates the jam attack output  252 . If this does not happen four times in succession, for example, on the third occasion the status is correct, then the monitor  200  resets the counter. 
         [0109]    Similarly, if when the second drive signal  244  goes inactive, the magnetic signal input  212  is already inactive, then the monitor  200  records this as a potential shielding attack and increments a counter. If this occurs four times in succession, then the monitor  200  activates the weak output  254 . If this does not happen four times in succession, for example, on the second occasion the status is correct, then the monitor  200  resets the counter. 
         [0110]    In this embodiment, if the jam attack signal  252  or the weak output  254  is active, then the card guide control circuit  180  (specifically, the firmware  262 ) transmits an alarm to the SST control program  184 . This causes the SST control program  184  to return the data card  42  to the customer then put the SST  150  out of service and send an alarm signal to a remote management centre (not shown) to request a visit from a service engineer. 
         [0111]    Another feature of this embodiment is that it can ascertain if the card reader guide  10  has been interfered with, for example, by removing the card reader guide  10  from the fascia  140  and replacing the card reader guide  10  with a false reader guide incorporating an alien reader. Once removed from the fascia  140 , the card reader guide  10  may be placed by a fraudster within the SST  150  so that it still sends signals to the card guide control circuit  180  but is not able to jam the alien reader because it is too far away from the alien reader. This embodiment detects this type of activity by correlating a signal from the card reader guide  10  with a signal from the card reader  170 , as will now be described with reference to  FIGS. 11 and 12 . 
         [0112]      FIG. 11  is a graph  270  illustrating a signal from the magnetic reader detector  30  while a customer&#39;s hand is present in the vicinity of the card reader guide  10 . 
         [0113]    As is shown in  FIG. 11 , there are two main areas where a signal is positive, namely, where the customer&#39;s hand is present at card insertion (region  272 ) and where the customer&#39;s hand is present at card removal (region  274 ). 
         [0114]    At the card insertion zone  272 , when the customer&#39;s hand approaches the card reader guide  10  to insert the data card  42 , the magnetic reader detector  30  generates a rising signal  280 ; whereas, when the customer&#39;s hand leaves the card reader guide  10  after inserting the data card  42 , the magnetic reader detector  30  generates a falling signal  282 . 
         [0115]    At the card removal zone  274 , when the customer&#39;s hand approaches the card reader guide  10  to remove the data card  42 , the magnetic reader detector  30  generates a rising signal  284 ; whereas, when the customer&#39;s hand leaves the card reader guide  10  after removing the data card  42 , the magnetic reader detector  30  generates a falling signal  286 . 
         [0116]      FIG. 12  is a flowchart  300  illustrating the operation of the SST control program  184  with respect to customer presence detection while a customer is inserting the data card  42 . These steps are performed concurrently with, and independently of, some of the steps performed by the card guide control circuit  180  of  FIG. 10 . 
         [0117]    Initially, the SST control program  184  executes an attract sequence (step  302 ) during which a screen is presented inviting a customer to insert his/her data card. 
         [0118]    The SST control program  184  awaits notification from software (drivers and/or service providers) associated with the card reader  170  that a data card has been received in the card reader  170  (step  304 ). 
         [0119]    Once a data card has been received, the SST control program  184  ascertains if a customer has been detected by the magnetic reader detector  30  (step  306 ). In this embodiment, this is implemented by the firmware  262  notifying the SST control program  184  when the jam signal (on output  220  from the detector  190 ) is active. This is because the jam signal is only active when the width switch is closed, the shutter is open, and the magnetic reader detector  30  detects the customer (and/or the customer&#39;s card). 
         [0120]    If a customer is detected (typically the customer&#39;s hand will still be sufficiently close to the card reader guide  10  to be detected by the magnetic reader detector  30 ) then the SST control program  184  resets a counter (step  308 ) and continues with the transaction as normal (step  310 ). 
         [0121]    If a customer is not detected then an alarm event is triggered by the SST control program  184  (step  312 ). 
         [0122]    The SST control program  184  then increments a counter (step  314 ) and ascertains if a predetermined criterion has been met (step  316 ). This predetermined criterion may be set so that a single alarm event will satisfy the criterion; alternatively, multiple consecutive alarm events may be required. In this embodiment, two successive alarm events are required (that is, two customers in a row must not be detected) before the SST control program  184  transmits an alarm to the remote management centre. 
         [0123]    If the predetermined criterion has not been met, then the transaction proceeds as normal (step  310 ). 
         [0124]    If the next customer is detected by the magnetic reader detector  30  then the SST control program  184  resets the counter (step  308 ) and proceeds with that transaction (step  310 ). 
         [0125]    If the next customer is not detected by the magnetic reader detector  30 , then the predetermined criterion will have been met (two successive customers not detected). In such an event, the SST control program  184  transmits an alarm signal to the remote management centre (step  318 ). 
         [0126]    The SST control program  184  then returns the data card  42  to the customer, terminates the transaction, and puts the SST  150  out of service (step  320 ) until a service engineer (dispatched by the remote management centre) visits the SST  150  and confirms that the card reader guide  10  is operating correctly and has not been moved. 
         [0127]    It should now be appreciated that this embodiment enables the SST  150  to ascertain if the card reader guide  10  has been removed by attempting to correlate a signal from the card reader guide  10  with a signal from the card reader  170 . 
         [0128]    Various modifications may be made to the above described embodiment within the scope of the invention, for example, in other embodiments, the number of inductive coil drives  120  may be more or less than two. In other embodiments, the inductive coil drives  120  may be driven at a frequency other than  2 kHz. 
         [0129]    In other embodiments, the number of times in succession that a correlation must be incorrect before the appropriate signal is activated may be more or less than four, and may differ for the jam attack output and the weak output. 
         [0130]    In other embodiments, the control circuit  180  may include a built-in alarm. 
         [0131]    In other embodiments the shape of the protrusions may differ from those described above. 
         [0132]    In other embodiments, the magnetic reader detector  30  may be located outside the card reader guide; for example, the magnetic reader detector  30  may be mounted directly onto the SST fascia. 
         [0133]    The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. 
         [0134]    The terms “comprising”, “including”, “incorporating”, and “having” are used herein to recite an open-ended list of one or more elements or steps, not a closed list. When such terms are used, those elements or steps recited in the list are not exclusive of other elements or steps that may be added to the list. 
         [0135]    Unless otherwise indicated by the context, the terms “a” and “an” are used herein to denote at least one of the elements, integers, steps, features, operations, or components mentioned thereafter, but do not exclude additional elements, integers, steps, features, operations, or components. 
         [0136]    The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other similar phrases in some instances does not mean, and should not be construed as meaning, that the narrower case is intended or required in instances where such broadening phrases are not used.