A telephone call processing system for processing telephone calls comprising voice signals and data signals between a caller and an agent, the system comprising: a first interface for receiving voice signals and data signals from the caller and a second interface for receiving voice signals and data signals from the agent, the first and second interfaces configured to selectively pass voice signals and data signals therebetween to enable communication between the caller and agent; attenuation means configured to selectively attenuate voice and data signals passing from the first interface to the second interface to impede the agent from receiving voice and data signals from the caller; detection means configured to detect and decode data signals received at the first interface; and a processor coupled to the attenuation means and detection means and configured to cause the detection means to begin detecting and decoding a string of discrete data signals from the caller, the string of discrete data signals having a length and conveying sensitive information; wherein whilst said string of discrete data signals is being received at the first interface, the telephone call processing system is configured to operate exclusively in each of: a first mode in which voice signals and data signals are permitted to pass from the first interface to the second interface to enable the agent to receive voice and data signals from the caller; and a second mode in which the processor causes the attenuation means to attenuate voice and data signals passing from the first interface to the second interface to impede the agent from receiving voice and data signals from the caller; wherein information represented by a subset of the string of discrete data signals is indicative of its length, and wherein the processor is configured to determine that length once the subset has been detected and decoded by the detection means. a first interface for receiving voice signals and data signals from the caller and a second interface for receiving voice signals and data signals from the agent, the first and second interfaces configured to selectively pass voice signals and data signals therebetween to enable communication between the caller and agent; attenuation means configured to selectively attenuate voice and data signals passing from the first interface to the second interface to impede the agent from receiving voice and data signals from the caller; detection means configured to detect and decode data signals received at the first interface; and a processor coupled to the attenuation means and detection means and configured to cause the detection means to begin detecting and decoding a string of discrete data signals from the caller, the string of discrete data signals having a length and conveying sensitive information; wherein whilst said string of discrete data signals is being received at the first interface, the telephone call processing system is configured to operate exclusively in each of: a first mode in which voice signals and data signals are permitted to pass from the first interface to the second interface to enable the agent to receive voice and data signals from the caller; and a second mode in which the processor causes the attenuation means to attenuate voice and data signals passing from the first interface to the second interface to impede the agent from receiving voice and data signals from the caller; a first mode in which voice signals and data signals are permitted to pass from the first interface to the second interface to enable the agent to receive voice and data signals from the caller; and a second mode in which the processor causes the attenuation means to attenuate voice and data signals passing from the first interface to the second interface to impede the agent from receiving voice and data signals from the caller;