This ‘one ring’ scam is known as a Wangiri, a Japanese term meaning one (ring) and cut. It occurs when a fraudster dials a range of numbers, often using an autodialling machine, usually from a different country, and the call will ‘hang up’ after approximately one ring. The fraudster's objective is for the person that missed the call to ring the number back. These tend to be high cost international numbers and they generate revenue for the fraudster. If the person does ring back, the fraudster attempts to keep the customer on the phone for as long as they can (to generate more revenue) and often use recorded messages to prolong the call. This is a known form of fraud worldwide.
Mobile operators’ advice for people who receive a missed call from an international number or a number that they do not recognise is not to call the number back. If it is a legitimate call, then the caller will likely call you back or they will leave a voicemail. Vigilance should be maintained for any call you receive from any unknown number, particularly an international number.
To protect customers against Wangiri, operators in the Irish market have implemented controls which allow mobile providers to block their customers from calling these numbers back.