Mobile phone customers of Vodafone and O2 are susceptible to a growing scam that allows criminals to gain access to their victims’ bank accounts.

An investigation by BBC One’s Watchdog Live found that the mobile giants were giving out replacement SIM cards to customers without conducting proper ID checks.

SIM-swap scams take place when criminals convince a mobile operator to provide them with replacement SIM cards by using a fake identity and pretending that their phone had been either stolen or lost, thereby gaining access to someone’s mobile phone number.

Criminals can accomplish this fraud by using the victim’s personal information stolen via cyberattacks or malware. Much of this information is available for sale on the dark web.

Once criminals have the replacement card, the victim’s SIM card no longer works. The criminals can then hijack texts and calls and access any of the victim’s online services that send security codes to his or her mobile phone, including bank accounts. This access can potentially allow the criminal to empty a victim’s account.

The investigation highlighted the case of a victim who lost £2,000 to a SIM-swap scam.

The staff at Three and EE stores always asked for an ID before they would give the investigator from Watchdog Live a replacement SIM card. However, five of six O2 stores and two Vodafone stores allowed the investigator to get a SIM card for somebody else’s mobile phone without asking for an ID.

Incidents of SIM-swap fraud have increased by 60% since 2016.